Photo-detecting apparatus with multi-reset mechanism

This patent application claims the benefit of U.S. Provisional Patent Application No. 62/778,291, filed Dec. 12, 2018, U.S. Provisional Patent Application No. 62/807,250, filed Feb. 19, 2019, U.S. Provisional Patent Application No. 62/875,941, filed Jul. 18, 2019, which are incorporated by reference herein.

1. Field of the Invention

The present invention relates to a photo-detecting apparatus, and more particularly, to a photo-detecting apparatus with a multi-reset mechanism.

2. Description of the Prior Art

Photo-detecting apparatus may be used to detect incident light and convert the incident light to electrical signal that may be further processed by another circuitry. Photodetectors may be used in consumer electronics products, image sensors, data communications, time-of-flight (ToF), light detection and ranging (LiDAR), medical devices, and many other suitable applications. However, when photodetectors are applied to these applications in a single or array configuration, the leakage current and dark current may degrade performances such as increasing the power consumption and reducing the signal to noise ratio.

According to a first aspect of the present application, a photo-detecting apparatus is provided. The photo-detecting apparatus includes an optical-to-electric converter, having a first output terminal, configured to convert an incident light to an electrical signal; a cascode transistor, having a control terminal, a first channel terminal and a second channel terminal, wherein the second channel terminal of the cascode transistor is coupled to the first output terminal of the optical-to-electric converter; and a reset transistor, having a control terminal, a first channel terminal and a second channel terminal, wherein the first channel terminal of the reset transistor is coupled to a supply voltage and the second channel terminal of the reset transistor is coupled to the first channel terminal of the cascode transistor.

In a further aspect of the present application, the optical-to-electric converter includes a light-absorption material formed on a semiconductor substrate, wherein the light absorption material is a material different from the semiconductor substrate.

In a further aspect of the present application, the optical-to-electric converter includes a photodiode configured to convert the incident light to the electrical signal; and a switch configured to output the electrical signal at the first output terminal according to a switch signal.

In a further aspect of the present application, the first output terminal of the optical-to-electric converter is substantially operated at a constant voltage.

In a further aspect of the present application, wherein the control terminal of the reset transistor is configured to receive a reset signal, the resetting times of the reset signal is equal to or greater than two during a formation of a subframe.

In a further aspect of the present application, the photo-detecting apparatus is configured to form a final 3D frame, wherein the final 3D frame is obtained according to a plurality of subframes.

Among other advantages and benefits of the embodiments disclosed herein, the embodiments provide a photo-detecting apparatus capable of absorbing a least a near-infrared (NIR) light or a short-wave infrared (SWIR) light efficiently. In some embodiments, the photo-detecting apparatus may have smaller chip size, low dark current and/or higher accuracy of the 3D image depth information, and low leakage current and/or lower consumption of the 3D image sensor power.

These and other objectives of the present disclosure will become obvious to those of ordinary skill in the art after reading the following detailed description of the alternative embodiments that are illustrated in the various figures and drawings.

These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings.

The foregoing aspects and many of the attendant advantages of this application will become more readily appreciated as the same becomes better understood by reference to the following detailed description, when taken in conjunction with the accompanying drawings, wherein:

FIG. 1A - FIG. 1J-4 illustrate the photo-detecting apparatuses and photo-detecting methods using one-tap configurations, according to some embodiments.

FIG. 2A - FIG. 2D-4 illustrate the photo-detecting apparatuses and photo-detecting methods using two-tap configurations, according to some embodiments.

FIG. 3A - FIG. 3B illustrate the photo-detecting apparatuses without cascode transistor, according to some embodiments.

FIG. 4A - FIG. 4C illustrate the timing diagrams applying multi-reset mechanisms, according to some embodiments.

General Structure of One-Tap Configuration

FIG. 1A illustrates a photo-detecting apparatus 100 A with one-tap configuration, according to some embodiments. The photo-detecting apparatus 100 A includes an optical-to-electric converter 170 , a cascode transistor 130 A, a reset transistor 141 A, a source-follower transistor 142 A, a row-select transistor 143 A, a capacitor 150 A and a bit-line BL-A.

The optical-to-electric converter 170 is configured to convert an incident light IL to an electrical signal IA 1 at an output terminal 110 A, where the electrical signal IA 1 is a photo-current. There are many implementations for the optical-to-electric converter 170 , the details will be described hereinafter. The cascode transistor 130 A is coupled between the optical-to-electric converter 170 and the reset transistor 141 A. Specifically, one channel terminal (e.g., source terminal) of the cascode transistor 130 A is coupled to the output terminal 110 A of the optical-to-electric converter 170 and the other channel terminal (e.g., drain terminal) of cascode transistor 130 A is coupled to one channel terminal (e.g., source terminal) of the reset transistor 141 A. In some implementations, cascode transistor 130 A, reset transistor 141 A, source-follower transistor 142 A and row-select transistor 143 A can be implemented by NMOS transistors or PMOS transistors.

During operation of the photo-detecting apparatus 100 A, the channel terminal 120 A on the capacitor 150 A is charged to a reset voltage VDDR through the reset transistor 141 A. For example, by applying a reset signal RST that causes the reset transistor 141 A to operate in the saturation or triode region, a current will flow through the reset transistor 141 A onto the capacitor 150 A and charge the capacitor 150 A to the reset voltage VDDR. Notably, the reset voltage VDDR can be the same or different with the supply voltage VDD.

Once the charging is completed, an integration of the electrical signal IA 1 generated by the optical-to-electric converter 170 may begin. The cascode transistor 130 A can be controlled to initiate and terminate the integration through a control voltage Vc 1 generated on the gate terminals of the cascode transistor 130 A. For example, the control voltage Vc 1 may be set to operate the cascode transistor 130 A in the subthreshold or saturation region so that the voltage VA 1 generated at terminal 110 A can be maintained at a nearly constant bias. As the voltage VA 1 generated at terminal 110 A is stable and relatively low, the dark current generated by the optical-to-electric converter 170 can be suppressed.

One-Tap ToF Application

FIG. 1B illustrates a photo-detecting apparatus 100 B with one-tap configuration, which is used in ToF application. Specifically, this embodiment shows a configuration of the optical-to-electric converter 170 , including a photodiode 172 , switch 171 A and 171 B.

In accordance with this embodiment, applying a switch signal TG 1 greater than the threshold voltage of the switch 171 A while applying a switch signal TG 2 lower than the threshold voltage of switch 171 B, the photo-generated carriers generated by the photodiode 172 will be directed to flow through the switch 171 A and the cascode transistor 130 A. Contrarily, applying a switch signal TG 2 greater than the threshold voltage of the switch 171 B while applying a switch signal TG 1 lower than the threshold voltage of switch 171 A, the photo-generated carriers generated by the photodiode 172 will be directed to flow through the switch 171 B.

In more detail, the switch signal TG 1 and the switch signal TG 2 are demodulation signals. In one implementation, the switch signal TG 1 and the switch signal TG 2 are differential to each other. In another implementation, the switch signal TG 1 and the switch signal TG 2 use clock signals with a 50% duty cycle. In other possible implementations, the duty cycle can be different (e.g., 30% duty cycle). In some implementations, square wave is used as the modulation and demodulation signals. In some implementations, sinusoidal wave is used as the modulation and demodulation signals instead of square wave.

During integration operation, the capacitor 150 A will be discharged when the switch signal TG 1 turns-on the switch 171 A and the incident light IL comes in. After a predetermined time of integration, the output voltage VOUT 1 will be dropped to a settled value. According to a selecting signal SelA, this settled value will be read-out onto the bit-line BL-A through the follower transistor 142 A and row-select transistor 143 A. By repeating the above procedure but with different modulation and/or demodulation phases, the system can determine a distance between a target object and the photo-detecting apparatus 100 B.

One-Tap ToF Application with Detailed Voltage Generator

In order to maintain the voltages VA 1 and VA 2 at a nearly constant bias, a voltage generator is implemented. Please refer to FIG. 1C , which illustrates an embodiment of a photo-detecting apparatus 100 C with a voltage generator 180 .

The voltage generator 180 is configured to bias the photo-detecting apparatus 100 C. In this embodiment, the voltage generator 180 can be an operational amplifier in which one output is coupled to the gain boost circuit 190 and generates a bias voltage Vop 1 , and another output is coupled to switch 171 B and generates a voltage VA 2 . Due to the drain of the switch 171 B is in a negative feedback to an input of the operational amplifier, the voltage VA 2 is substantially equal to the reference voltage Vref.

The gain boost circuit 190 includes transistors 144 A and 145 A, where the transistor 145 A and the cascode transistor 130 A collectively forma feedback circuit and accordingly increase a gain of the cascode transistor 130 A. The voltage generator 180 generates the bias voltage Vop 1 on the transistor 144 A of the gain boost circuit 190 so as to adjust the control voltage VC 1 and make the voltage VA 1 being substantially equal to bias voltage VA 2 . Consequently, the voltages VA 1 and VA 2 are substantially equal to the reference voltage Vref.

This embodiment illustrates a one-tap photo-detecting apparatus 100 C with an exemplary voltage generator 180 . One may implement other voltage generator 180 to control the voltages VA 1 and VA 2 to reduce the dark-current generated by the optical-to-electric converter 170 .

FIG. 1D illustrates a photo-detecting apparatus 100 D with a cross-sectional view of a portion of the optical-to-electric converter 170 . The photodiode 172 , in this embodiment, is a vertical-type photodiode, where a N-doped region N+ and a P-doped region P+ are configured in a vertical direction, and a light-absorption material (e.g., germanium Ge or germanium-silicon GeSi) is formed in-between the N-doped region N+ and the P-doped region P+. In some implementations, the light-absorption material formed in-between the N-doped region N+ and the P-doped region P+ is supported by the semiconductor substrate (e.g., silicon Si or silicon-germanium SiGe). On the other hands, in one implementation, the switches 171 A and 171 B and the photodiode 172 can be manufactured in the same chip, the rest of the elements can be manufactured in another chip. In one implementation, the photodiode 172 can be manufactured in one chip, the rest of the elements can be manufactured in another chip. In one implementation, all the elements shown in FIG. 1D can be manufactured in the same chip. Furthermore, the optical-to-electric converter 170 can be implemented by back-side incident (BSI) or front-side incident (FSI), which means the light IL can be received from the bottom of the chip or top of the chip.

FIG. 1E illustrates a photo-detecting apparatus 100 E with a cross-sectional view of a portion of the optical-to-electric converter 170 . The photodiode 172 , in this embodiment, is a horizontal-type photodiode, where a N-doped region N+ and a P-doped region P+ are configured in a horizontal direction, and a light-absorption material (e.g., germanium Ge or germanium-silicon GeSi) covers the N-doped region N+ and the P-doped region P+. In some implementations, the light-absorption material covers the N-doped region N+ and the P-doped region P+ at its surface, and is supported by the semiconductor substrate (e.g., silicon Si or silicon-germanium SiGe). On the other hands, in one implementation, the switches 171 A and 171 B and the photodiode 172 can be manufactured in the same chip, the rest of the elements can be manufactured in another chip. In one implementation, the photodiode 172 can be manufactured in one chip, the rest of the elements can be manufactured in another chip. In one implementation, all the elements shown in FIG. 1E can be manufactured in the same chip. Furthermore, the optical-to-electric converter 170 can be implemented by back-side incident (BSI) or front-side incident (FSI), which means the light IL can be received from the bottom of the chip or top of the chip.

FIG. 1F-1 illustrates a photo-detecting apparatus 100 F with a cross-sectional view of a portion of the optical-to-electric converter 170 . The photodiode 172 and switch 171 B can be integrated and laid out as shown in the block 1721 B of FIG. 1F-1 , where a light-absorption material (e.g., germanium Ge or germanium-silicon GeSi) covers these N-doped regions N+ and the P-doped regions P+. In some implementations, the light-absorption material covers the N-doped regions N+ and the P-doped regions P+ at its surface, and is supported by the semiconductor substrate (e.g., silicon Si or silicon-germanium SiGe). On the other hands, in one implementation, the switches 171 A and 171 B and the photodiode 172 can be manufactured in the same chip, the rest of the elements can be manufactured in another chip. In one implementation, the photodiode 172 can be manufactured in one chip, the rest of the elements can be manufactured in another chip. In one implementation, all the elements shown in FIG. 1F-1 can be manufactured in the same chip. Furthermore, the optical-to-electric converter 170 can be implemented by back-side incident (BSI) or front-side incident (FSI), which means the light IL can be received from the bottom of the chip or top of the chip.

FIG. 1F-2 illustrates a top view of the layout of photodiode 172 and switch 171 B embodied in photo-detecting apparatus 100 F. This layout 1721 B includes photodiode 172 and switch 171 B. As illustrated in FIG. 1F-2 , the profile of these doped regions is a ring and its cross-sectional view (line AA′) corresponds to the layout 1721 B of FIG. 1F-1 .

FIG. 1G illustrates a photo-detecting apparatus 100 G with a cross-sectional view of the optical-to-electric converter 170 . As illustrated in FIG. 1G , the optical-to-electric converter 170 includes switches 171 A and 171 B, and alight-absorption material (e.g., germanium Ge or germanium-silicon GeSi) is supported by the semiconductor substrate (e.g., silicon Si or silicon-germanium SiGe). The light-absorption material can use the material different from the semiconductor substrate. Each switch includes a terminal for receiving a demodulation signal and a terminal for outputting an electrical signal. For example, switch 171 A includes a terminal for receiving the demodulation signal TG 1 and a terminal for outputting the electrical signal IA 1 ; and switch 171 B includes a terminal for receiving the demodulation signal TG 2 and a terminal for outputting the electrical signal IA 2 . In some implementations, the terminals for receiving the demodulation signal is highly-doped with P-type dopants; the terminals for outputting the electrical signal is highly-doped with N-type dopants.

FIG. 1H illustrates a photo-detecting apparatus 100 H with a cross-sectional view of the optical-to-electric converter 170 . As illustrated in FIG. 1H , the optical-to-electric converter 170 includes switches 171 A and 171 B, and alight-absorption material (e.g., germanium Ge or germanium-silicon GeSi) is supported by the semiconductor substrate (e.g., silicon Si or silicon-germanium SiGe). The light-absorption material can use the material different from the semiconductor substrate. Each switch includes a terminal for receiving a demodulation signal and a terminal for outputting an electrical signal. For example, switch 171 A includes a terminal for receiving the demodulation signal TG 1 and a terminal for outputting the electrical signal IA 1 ; and switch 171 B includes a terminal for receiving the demodulation signal TG 2 and a terminal for outputting the electrical signal IA 2 . Compared to FIG. 1G , the terminal of switch 171 A for receiving the demodulation signal TG 1 has no additional doping or is lightly-doped with P-type or N-type dopants, and the terminal of switch 171 B for receiving the demodulation signal TG 2 has no additional doping or is lightly-doped with P-type or N-type dopants.

One-Tap Optical Switch Application

Optical switch may also be used in one-tap photo-detecting apparatus. FIG. 1I-1 illustrates a photo-detecting apparatus 100 I with optical switch. As shown in FIG. 1I-1 , optical-to-electric converter 170 includes an optical switch 1701 and a photodiode 1702 . The optical switch 1701 is configured to gate or pass the incident light IL and the photodiode 1702 is configured to convert the light passed by the optional switch 1701 into the electrical signal IA 1 . The detail implementation will be described below.

FIG. 1I-2 illustrates an embodiment of optical switch 1701 . Optical switch 1701 includes an electro-absorption material 17011 , an optional transparent insulating material 17012 and a transparent conductive material 17013 . The electro-absorption material 17011 is positioned in-between two transparent conductive materials 17013 with optional transparent insulating materials 17012 . Optional transparent insulating material 17012 is an optional element, one may use or remove this material based on the design requirements. In some implementations, the electro-absorption material 17011 can be organic/inorganic semiconductor or quantum well/dot; the optional transparent insulating material 17012 can be oxide or polymer; and the transparent conductive materials 17013 can be fluorine/indium doped tin oxide. Furthermore, by properly patterning of the transparent conductive material 17013 it is possible to avoid excess capacitance and so to lower demodulating energy. During operation, transparent conductive materials 17013 will be biased by a control signal CS 1 to control whether the incident light IL passes the optical switch 1701 . For example, when the control signal CS 1 is operated at a first bias, the incident light IL passes the optical switch 1701 . Oppositely, when the control signal CS 1 is operated at a second bias, the incident light IL may be absorbed by the electro-absorption material 17011 or being reflected so that the incident light IL cannot pass the optical switch 1701 .

FIG. 1I-3 illustrates an embodiment of photodiode 1702 . The photodiode 172 , in this embodiment, is a vertical-type photodiode, where a first doped region 17015 and a second doped region 17016 are configured in a vertical direction, and a light-absorption material 170 A 1 (e.g., germanium Ge or silicon-germanium SiGe) is formed in-between the first doped region 17015 and the second doped region 17016 . In some implementations, the light-absorption material 170 A 1 formed in-between the first doped region 17015 and the second doped region 17016 , which is supported by the semiconductor substrate (e.g., silicon Si or silicon-germanium SiGe). The polarities of the first doped region 17015 and the second doped region 17016 are different. In one implementation, the first doped region 17015 is N-doped region and second doped region 17016 is P-doped region. In another implementation, the first doped region 17015 is P-doped region and second doped region 17016 is N-doped region.

FIG. 1I-4 illustrates an embodiment of photodiode 1702 . The photodiode 172 , in this embodiment, is a horizontal-type photodiode, where the first doped region 17015 and the second doped region 17016 are configured in a horizontal direction, and the light-absorption material 170 A 1 (e.g., germanium Ge or germanium-silicon GeSi) covers the first doped region 17015 and the second doped region 17016 . In some implementations, the light-absorption material 170 A 1 is supported by the semiconductor substrate (e.g., silicon Si or silicon-germanium). The polarities of the first doped region 17015 and the second doped region 17016 are different. In one implementation, the first doped region 17015 is N-doped region and second doped region 17016 is P-doped region. In another implementation, the first doped region 17015 is P-doped region and second doped region 17016 is N-doped region.

FIG. 1I-5 illustrates an operation of the optical-to-electric converter 170 depicted in FIG. 1I-1 according to an embodiment. This operation includes the steps of receiving an incident light IL by a first optics (step S 11 ), passing the incident light IL at a first bias, and absorbing or reflecting the incident light IL at a second bias by the optical switch 1701 (step S 12 ), outputting the incident light IL passed by the optical switch 1701 by a second optics (step S 13 ) and converting the passed incident light IL into the electrical signal IA 1 by the photodiode 1702 (step S 14 ). The first optics and second optics may include micro-lens, bandpass filter, partial mirror, grating, diffusor, etc. It is noted that the first optics and second optics are optional elements, and one may use or not use these optics depend on the design requirements.

One-Tap CIS Application

One-tap configuration can be used in CMOS image sensor (CIS), which is a two-dimensional (2D) sensing. As shown in FIG. 1J-1 , similar to above-mentioned ToF architecture, a photo-detecting apparatus 100 J used in CMOS image sensor includes an optical-to-electric converter 170 , a cascode transistor 130 A, a reset transistor 141 A, a capacitor 150 A, a source-follower transistor 142 A, a row-select transistor 143 A and a bit-line BL-A. In this embodiment, the optical-to-electric converter 170 includes a photodiode 172 and a switch 171 A. The photodiode 172 is configured to convert an incident light IL to an electrical signal IA, which is a photo-current. The switch 171 A is configured to output the electrical signal IA 1 to the cascode transistor 130 A according to a switch signal TG 1 , where the electrical signal IA will be generated when the switch signal TG 1 turns-on the switch 171 A.

At beginning, the reset signal RST resets the output voltage VOUT 1 to the reset voltage VDDR. When the switch signal TG 1 turns-on the switch 171 A, the electrical signal IA 1 is generated, the output voltage VOUT 1 on the capacitor 150 A will drop until the switch signal TG 1 turns-off the transistor 171 A. Compared to ToF application, the switch signal TG 1 used in 2D sensing application turns-on the switch 171 A for a longer time period (e.g., 100 μs, 500 μs, 1 ms, 5 ms, or similar time scales) to absorb the incident light IL, instead of using a fast demodulation signal (e.g., 3 ns, 10 ns, 30 ns, 100 ns or similar time scales).

The cascode transistor 130 A is configured as a buffer, which is coupled between the optical-to-electric converter 170 and the reset transistor 141 A. Specifically, the channel terminal (e.g., drain terminal) of the cascode transistor 130 A is coupled to the channel terminal (e.g., source terminal) of the reset transistor 141 A, and the channel terminal (e.g., source terminal) of the cascode transistor 130 A is coupled to channel terminal (e.g., drain terminal) of the transistor ( 171 A). The control terminal (e.g., gate terminal) of the cascode transistor 130 A is coupled to a control voltage VC 1 . In some implementations, switch 171 A, cascode transistor 130 A, reset transistor 141 A, source-follower transistor 142 A and row-select transistor 143 A can be implemented by NMOS transistors or PMOS transistors.

Since the cascode transistor 130 A is coupled between the output terminal 110 A of the optical-to-electric converter 170 and the channel terminal (e.g., source terminal) of the reset transistor 141 A, the output terminal 110 A of the optical-to-electric converter 170 and the channel terminal (e.g., source terminal) of the reset transistor 141 A are separated when the cascode 130 A transistor is operated in the saturation or the subthreshold region. The voltage VA 1 generated on the output terminal 110 A of the optical-to-electric converter 170 can be controlled or biased at a constant voltage VA 1 to reduce the dark current generated by the optical-to-electric converter 170 .

In one implementation, the control terminal (e.g., gate terminal) of the cascode transistor 130 A and the control terminal (e.g. gate terminal) of the transistor 171 A can be coupled to each other, meaning the control voltage VC 1 and the switch signal TG 1 are the same, which is a signal for switching on/off the cascode transistor 130 A and transistor 171 A.

In one implementation, the control terminal (e.g., gate terminal) of the cascode transistor 130 A and the control terminal (e.g., gate terminal) of the transistor 171 A can be separated, meaning the control voltage VC 1 and the switch signal TG 1 are different, in which the control voltage VC 1 is a constant voltage and the switch signal TG 1 is a signal for switching on/off the transistor 171 A.

The source-follower transistor 142 A and the row-select transistor 143 A are configured to read out the output voltage VOUT 1 to the bit-line BL-A according to the selecting signal SelA.

FIG. 1J-2 illustrates the photo-detecting apparatus 100 J with a structural view of the photodiode 172 . The photodiode 172 , in this embodiment, is a vertical-type photodiode, where a N-doped region N+ and a P-doped region P+ are configured in a vertical direction, and a light-absorption material (e.g., germanium Ge or germanium-silicon GeSi) is formed in-between the N-doped region N+ and the P-doped region P+. In some implementations, the light-absorption material formed in-between the N-doped region N+ and the P-doped region P+ is supported by the semiconductor substrate (e.g., silicon Si or SiGe silicon-germanium). On the other hands, in one implementation, the switch 171 A and the photodiode 172 can be manufactured in the same chip, the rest of the elements can be manufactured in another chip. In one implementation, the photodiode 172 can be manufactured in one chip, the rest of the elements can be manufactured in another chip. In one implementation, all the elements shown in FIG. 1J-2 can be manufactured in the same chip. Furthermore, the optical-to-electric converter 170 can be implemented by back-side incident (BSI) or front-side incident (FSI), which means the light IL can be received from the bottom of the chip or top of the chip.

FIG. 1J-3 illustrates the photo-detecting apparatus 100 J with a structural view of the photodiode 172 . The photodiode 172 , in this embodiment, is a horizontal-type photodiode, where a N-doped region N+ and a P-doped region P+ are configured in a horizontal direction, and a light-absorption material (e.g., germanium Ge or germanium-silicon GeSi) covers the N-doped region N+ and the P-doped region P+. In some implementations, the light-absorption material covers the N-doped region N+ and the P-doped region P+ at its surface, and is supported by the semiconductor substrate (e.g., silicon Si or silicon-germanium). On the other hands, in one implementation, the switch 171 A and the photodiode 172 can be manufactured in the same chip, the rest of the elements can be manufactured in another chip. In one implementation, the photodiode 172 can be manufactured in one chip, the rest of the elements can be manufactured in another chip. In one implementation, all the elements shown in FIG. 1J-3 can be manufactured in the same chip. Furthermore, the optical-to-electric converter 170 can be implemented by back-side incident (BSI) or front-side incident (FSI), which means the light IL can be received from the bottom of the chip or top of the chip.

FIG. 1J-4 illustrates the photo-detecting apparatus 100 J with a structural view of the photodiode 172 . The photodiode 172 , in this embodiment, is a horizontal-type photodiode, where a N-doped region N+ and a P-doped region P+ are configured in a horizontal direction. Compared to FIG. 1J-3 , this embodiment uses silicon semiconductor substrate as a light-absorption material. On the other hands, in one implementation, the switch 171 A and the photodiode 172 can be manufactured in the same chip, the rest of the elements can be manufactured in another chip. In one implementation, the photodiode 172 can be manufactured in one chip, the rest of the elements can be manufactured in another chip. In one implementation, all the elements shown in FIG. 1J-4 can be manufactured in the same chip. Furthermore, the optical-to-electric converter 170 can be implemented by back-side incident (BSI) or front-side incident (FSI), which means the light IL can be received from the bottom of the chip or top of the chip.

FIG. 1A to FIG. 1J-4 illustrate the photo-detecting apparatuses with one-tap configuration, which can be used in 3D sensing application (e.g., ToF applications) or 2D sensing application (e.g., CIS applications). 3D sensing application uses demodulation signal to obtain the image depth information. However, 2D sensing application uses non-demodulation signal to obtain the image intensity information. Furthermore, two-tap configuration is also an alternative embodiment for performing photo-detecting function, and the relevant details will be described below.

General Structure of Two-Tap Configuration

FIG. 2A illustrates a photo-detecting apparatus 200 A with two-tap configuration, according to some embodiments. The photo-detecting apparatus 200 A includes an optical-to-electric converter 170 , cascode transistors 130 A and 130 B, reset transistors 141 A and 141 B, source-follower transistors 142 A and 142 B, row-select transistors 143 A and 143 B, capacitors 150 A and 150 B, and bit-lines BL-A and BL-B. Compared to FIG. 1A , the photo-detecting apparatus 100 A with one-tap configuration is an unsymmetrical structure, however, the photo-detecting apparatus 200 A with two-tap configuration is a symmetrical structure.

The optical-to-electric converter 170 is configured to convert an incident light IL to an electrical signal IA 1 at an output terminal 110 A and an electrical signal IA 2 at an output terminal 110 B, where the electrical signal IA 1 and the electrical signal IA 2 are photo-currents. There are many implementations for the optical-to-electric converter 170 , the details will be described hereinafter. The cascode transistor 130 A is coupled between the optical-to-electric converter 170 and the reset transistor 141 A. Specifically, one channel terminal (e.g., source terminal) of the cascode transistor 130 A is coupled to the output terminal 110 A of the optical-to-electric converter 170 and the other channel terminal (e.g., drain terminal) of cascode transistor 130 A is coupled to one channel terminal (e.g., source terminal) of the reset transistor 141 A. Similarly, the cascode transistor 130 B is coupled between the optical-to-electric converter 170 and the reset transistor 141 B. Specifically, one channel terminal (e.g., source terminal) of the cascode transistor 130 B is coupled to the output terminal 110 B of the optical-to-electric converter 170 and the other channel terminal (e.g., drain terminal) of cascode transistor 130 B is coupled to one channel terminal (e.g., source terminal) of the reset transistor 141 B. In some implementations, cascode transistors 130 A and 130 B, reset transistors 141 A and 141 B, source-follower transistors 142 A and 142 B, and row-select transistors 143 A and 143 B can be implemented by NMOS transistors or PMOS transistors.

During operation of the photo-detecting apparatus 100 B, the channel terminal 120 A on the capacitor 150 A is charged to a reset voltage VDDR through the reset transistor 141 A. For example, by applying a reset signal RST that causes the reset transistor 141 A to operate in the saturation or triode region, a current will flow through the reset transistor 141 A onto the capacitor 150 A and charge the capacitor 150 A to the reset voltage VDDR. Similarly, the channel terminal 120 B on the capacitor 150 B is charged to the reset voltage VDDR through the reset transistor 141 B. For example, by applying the reset signal RST that causes the reset transistor 141 B to operate in the saturation or triode region, a current will flow through the reset transistor 141 B onto the capacitor 150 B and charge the capacitor 150 B to the reset voltage VDDR. It is noted that the reset voltage VDDR can be the same or different with the supply voltage VDD.

Once the charging is completed, an integration of the electrical signals IA 1 and IA 2 generated by the optical-to-electric converter 170 may begin. The cascode transistor 130 A can be controlled to initiate and terminate the integration through a control voltage Vc 1 generated on the gate terminals of the cascode transistor 130 . For example, the control voltage Vc 1 may be set to operate the cascode transistor 130 in the subthreshold or saturation region so that the voltage VA 1 generated at terminal 110 A can be maintained at a nearly constant bias. Similarly, the cascode transistor 130 B can be controlled to initiate and terminate the integration through a control voltage Vc 2 generated on the gate terminals of the cascode transistor 130 B. For example, the control voltage Vc 2 may be set to operate the cascode transistor 130 B in the subthreshold or saturation region so that the voltage VA 2 generated at terminal 110 B can be maintained at a nearly constant bias. As the voltages VA 1 and VA 2 generated at terminal 110 A and terminal 110 B are stable and relatively low, the dark current generated by the optical-to-electric converter 170 can be suppressed.

Two-Tap ToF Application

FIG. 2B illustrates a photo-detecting apparatus 200 B with two-tap configuration, which is used in ToF application. Specifically, this embodiment shows a configuration of the optical-to-electric converter 170 , including a photodiode 172 , switches 171 A and 171 B.

In accordance with this embodiment, applying a switch signal TG 1 greater than the threshold voltage of the switch 171 A while applying a switch signal TG 2 lower than the threshold voltage of switch 171 B, the photo-generated carriers generated by the photodiode 172 will be directed to flow through the cascode transistor 130 A. Contrarily, applying a switch signal TG 2 greater than the threshold voltage of the switch 171 B while applying a switch signal TG 1 lower than the threshold voltage of switch 171 A, the photo-generated carriers generated by the photodiode 110 will be directed to flow through the cascode transistor 130 B.

In more detail, the switch signal TG 1 and the switch signal TG 2 are demodulation signals. In one implementation, the switch signal TG 1 and the switch signal TG 2 are differential to each other. In another implementation, the switch signal TG 1 and the switch signal TG 2 use clock signals with a 50% duty cycle. In other possible implementations, the duty cycle can be different (e.g., 30% duty cycle). In some implementations, square wave is used as the modulation and demodulation signals. In some implementations, sinusoidal wave is used as the modulation and demodulation signals instead of square wave.

During integration operation, the capacitor 150 A will be discharged when the switch signal TG 1 turns-on the switch 171 A and the incident light IL comes in. Similarly, the capacitor 150 B will be discharged when the switch signal TG 2 turns-on the switch 171 B and the incident light IL comes in. Thus, the photo-current IA 1 and the photo-current IA 2 are generated in-turn during integration operation. After a predetermined time of integration, the output voltage VOUT 1 will be dropped to a settled value and the output voltage VOUT 2 will be dropped to another settled value. According to a selecting signals SelA and SelB, the settled value of the output voltage VOUT 1 will be read-out onto the bit-line BL-A through the source-follower transistor 142 A and row-select transistor 143 A, and the settled value of the output voltage VOUT 2 will be read-out onto the bit-line BL-B through the source-follower transistor 142 B and row-select transistor 143 B. By repeating the above procedure but with different modulation and/or demodulation phases the system can determine a distance between a target object and the photo-detecting apparatus 200 B.

There are many implementations for optical-to-electric converter 170 of photo-detecting apparatus 200 B. For example, the optical-to-electric converter 170 of photo-detecting apparatus 200 B can use the embodiments of optical-to-electric converter 170 illustrated in FIG. 1D to FIG. 1H . One may use other embodiments to implement optical-to-electric converter 170 as well.

Two-Tap Optical Router Application

FIG. 2C illustrates a photo-detecting apparatus 200 C with optical router. As shown in FIG. 2C , optical-to-electric converter 170 includes an optical router 1703 and photodiodes 1704 and 1705 . The optical router 1703 is configured to direct the incident light IL to the photodiode 1704 or the photodiode 1705 so that the photodiode 1704 and photodiode 1705 convert the incident light IL into the electrical signals IA 1 and IA 2 respectively.

The optical router 1703 of the photo-detecting apparatus 200 C can be implemented by utilizing liquid crystals, pn/pin junctions, MEMS (micro-electrical-mechanical-system) capacitors, thermal heating pads, nonlinear crystals with 2 nd or 3 rd order of nonlinearity or other active means to direct the incident light IL through a free-space or a dielectric-space or a PIC (photonic integrated circuit) to the photodiode 1704 or the photodiode 1705 .

Two-Tap CIS Application

Two-tap configuration can be used in CMOS image sensor (CIS), which is a two-dimensional (2D) sensing. As shown in FIG. 2D-1 , a photo-detecting apparatus 200 D used in CMOS image sensor includes an optical-to-electric converter 170 , cascode transistors 130 A and 130 B, reset transistors 141 A and 141 B, source-follower transistors 142 A and 142 B, row-select transistors 143 A and 143 B, capacitors 150 A and 150 B, and bit-lines BL-A and BL-B.

Compared to the photo-detecting apparatus 200 B of FIG. 2B , the structure of photo-detecting apparatus 200 D and the structure of photo-detecting apparatus 200 B are the same. However, their operations are different.

At beginning, the reset signal RST resets the output voltage VOUT 1 to the reset voltage VDDR and the output voltage VOUT 2 to the reset voltage VDDR. When the switch signal TG 1 turns-on the switch 171 A, the electrical signal IA 1 is generated, the output voltage VOUT 1 on the capacitor 150 A will drop until the switch signal TG 1 turns-off the transistor ( 171 A). Similarly, when the switch signal TG 2 turns-on the switch 171 B, the electrical signal IA 2 is generated, the output voltage VOUT 2 on the capacitor 1502 will drop until the switch signal TG 2 turns-off the transistor ( 171 B).

Compared to ToF application, the switch signals TG 1 and TG 2 used in 2D sensing application can turns-on the switches 171 A and 171 B simultaneously for a longer time period (e.g., 100 μs, 500 μs, 1 ms, 5 ms, or similar time scales) to absorb the incident light IL, instead of using demodulation signal. In other words, the right-hand side circuit RS and left-hand side circuit LS can be symmetrically operated. In other implementation, the right-hand side circuit RS and left-hand side circuit LS can be independently operated. The photo-detecting apparatus 200 D can turns-on either switch 171 A or switch 171 B for a longer time period (e.g., 100 μs, 500 μs, 1 ms, 5 ms, or similar time scales), instead of using demodulation signal, to absorb the incident light IL to perform 2D sensing. In other words, one of the right-hand side circuit RS and left-hand side circuit LS is disable.

The cascode transistors 130 A is configured as a buffer, which is coupled between the optical-to-electric converter 170 and the reset transistor 141 A. Specifically, the channel terminal (e.g., drain terminal) of the cascode transistor 130 A is coupled to the channel terminal (e.g., source terminal) of the reset transistor 141 A, and the channel terminal (e.g., source terminal) of the cascode transistor 130 A is coupled to channel terminal (e.g., drain terminal) of the transistor 171 A. The control terminal (e.g., gate terminal) of the cascode transistor 130 A is coupled to a control voltage VC 1 . In some implementations, switch 171 A, cascode transistor 130 A, reset transistor 141 A, source-follower transistor 142 A and row-select transistor 143 A can be implemented by NMOS transistors or PMOS transistors.

Similarly, the cascode transistors 130 B is configured as a buffer, which is coupled between the optical-to-electric converter 170 and the reset transistor 141 B. Specifically, the channel terminal (e.g., drain terminal) of the cascode transistor 130 B is coupled to the channel terminal (e.g., source terminal) of the reset transistor 141 B, and the channel terminal (e.g., source terminal) of the cascode transistor 130 B is coupled to channel terminal (e.g., drain terminal) of the transistor 171 B. The control terminal (e.g., gate terminal) of the cascode transistor 130 A is coupled to a control voltage VC 2 . In some implementations, switch 171 B, cascode transistor 130 B, reset transistor 141 B, source-follower transistor 142 B and row-select transistor 143 B can be implemented by NMOS transistors or PMOS transistors.

Since the cascode transistor 130 A is coupled between the output terminal 110 A of the optical-to-electric converter 170 and the channel terminal (e.g., source terminal) of the reset transistor 141 A, the output terminal 110 A of the optical-to-electric converter 170 and the channel terminal (e.g., source terminal) of the reset transistor 141 A are separated when the cascode 130 A transistor is operated in the saturation or the subthreshold region. The voltage VA 1 generated on the output terminal 110 A of the optical-to-electric converter 170 can be controlled or biased at a constant voltage VA 1 to reduce the dark current generated by the optical-to-electric converter 170 .

Similarly, since the cascode transistor 130 B is coupled between the output terminal 110 B of the optical-to-electric converter 170 and the channel terminal (e.g., source terminal) of the reset transistor 141 B, the output terminal 110 B of the optical-to-electric converter 170 and the channel terminal (e.g., source terminal) of the reset transistor 141 A are separated when the cascode 130 B transistor is operated in the saturation or the subthreshold region. The voltage VA 2 generated on the output terminal 110 B of the optical-to-electric converter 170 can be controlled or biased at a constant voltage VA 2 to reduce the dark current generated by the optical-to-electric converter 170 .

In one implementation, the control terminal (e.g., gate terminal) of the cascode transistor 130 A and the control terminal (e.g. gate terminal) of the transistor 171 A can be coupled to each other, meaning the control voltage VC 1 and the switch signal TG 1 are the same, which is a signal for switching on/off the cascode transistor 130 A and transistor 171 A.

Similarly, in one implementation, the control terminal (e.g., gate terminal) of the cascode transistor 130 B and the control terminal (e.g. gate terminal) of the transistor 171 B can be coupled to each other, meaning the control voltage VC 2 and the switch signal TG 2 are the same, which is a signal for switching on/off the cascode transistor 130 A and transistor 171 A.

In one implementation, the control terminal (e.g., gate terminal) of the cascode transistor 130 A and the control terminal (e.g., gate terminal) of the transistor 171 A can be separated, meaning the control voltage VC 1 and the switch signal TG 1 are different, in which the control voltage VC 1 is a constant voltage and the switch signal TG 1 is a signal for switching on/off the transistor 171 A.

Similarly, in one implementation, the control terminal (e.g., gate terminal) of the cascode transistor 130 B and the control terminal (e.g., gate terminal) of the transistor 171 B can be separated, meaning the control voltage VC 2 and the switch signal TG 2 are different, in which the control voltage VC 2 is a constant voltage and the switch signal TG 2 is a signal for switching on/off the transistor 171 A.

The source-follower transistor 142 A and the row-select transistor 143 A are configured to read out the output voltage VOUT 1 to the bit-line BL-A according to the selecting signal SelA.

Similarly, the source-follower transistor 142 B and the row-select transistor 143 B are configured to read out the output voltage VOUT 2 to the bit-line BL-B according to the selecting signal SelB.

FIG. 2D-2 illustrates the photo-detecting apparatus 200 D with a structural view of the photodiode 172 . The photodiode 172 , in this embodiment, is a vertical-type photodiode, where a N-doped region N+ and a P-doped region P+ are configured in a vertical direction, and a light-absorption material (e.g., germanium Ge or germanium-silicon GeSi) is formed in-between the N-doped region N+ and the P-doped region P+. In some implementations, the light-absorption material formed in-between the N-doped region N+ and the P-doped region P+ is supported by the semiconductor substrate (e.g., silicon Si or silicon-germanium SiGe). On the other hands, in one implementation, the switch 171 A, switch 171 B and the photodiode 172 can be manufactured in the same chip, the rest of the elements can be manufactured in another chip. In one implementation, the photodiode 172 can be manufactured in the one chip, the rest of the elements can be manufactured in another chip. In one implementation, all the elements shown in FIG. 2D-2 can be manufactured in the same chip. Furthermore, the optical-to-electric converter 170 can be implemented by back-side incident (BSI) or front-side incident (FSI), which means the light IL can be received from the bottom of the chip or top of the chip.

FIG. 2D-3 illustrates the photo-detecting apparatus 200 D with a structural view of the photodiode 172 . The photodiode 172 , in this embodiment, is a horizontal-type photodiode, where a N-doped region N+ and a P-doped region P+ are configured in a horizontal direction, and a light-absorption material (e.g., germanium Ge) covers the N-doped region N+ and the P-doped region P+. In some implementations, the light-absorption material covers the N-doped region N+ and the P-doped region P+ at its surface, and is supported by the semiconductor substrate (e.g., silicon Si or silicon-germanium SiGe). On the other hands, in one implementation, the switch 171 A, the switch 171 B and the photodiode 172 can be manufactured in the same chip, the rest of the elements can be manufactured in another chip. In one implementation, the photodiode 172 can be manufactured in one chip, the rest of the elements can be manufactured in another chip. In one implementation, all the elements shown in FIG. 2D-3 can be manufactured in the same chip. Furthermore, the optical-to-electric converter 170 can be implemented by back-side incident (BSI) or front-side incident (FSI), which means the light IL can be received from the bottom of the chip or top of the chip.

FIG. 2D-4 illustrates the photo-detecting apparatus 200 D with a structural view of the photodiode 172 . The photodiode 172 , in this embodiment, is a horizontal-type photodiode, where a N-doped region N+ and a P-doped region P+ are configured in a horizontal direction. Compared to FIG. 1D-3 , this embodiment uses silicon semiconductor substrate as a light-absorption material. On the other hands, in one implementation, the switch 171 A, 171 B and the photodiode 172 can be manufactured in the same chip, the rest of the elements can be manufactured in another chip. In one implementation, the photodiode 172 can be manufactured in one chip, the rest of the elements can be manufactured in another chip. In one implementation, all the elements shown in FIG. 2D-4 can be manufactured in the same chip. Furthermore, the optical-to-electric converter 170 can be implemented by back-side incident (BSI) or front-side incident (FSI), which means the light IL can be received from the bottom of the chip or top of the chip.

FIG. 2A to FIG. 2D-4 illustrate the photo-detecting apparatuses with two-tap configuration, which can be used in 3D sensing application (e.g., ToF applications) or 2D sensing application (e.g., CIS applications). 3D sensing application uses demodulation signal to obtain the image depth information. However, 2D sensing application uses non-demodulation signal to obtain the image intensity information.

Other Implementations

The photo-detecting apparatuses mentioned above include a cascode transistor (e.g., cascode transistor 130 A or 130 B) coupled between the optical-to-electric converter 170 and reset transistor (e.g., reset transistor 141 A or 141 B). In some implementations, the cascode transistor can be removed as illustrated in FIG. 3A and FIG. 3B . FIG. 3A is a photo-detecting apparatus 300 A with one-tap configuration and FIG. 3B is a photo-detecting apparatus 300 B with two-tap configuration. Similarly, the photo-detecting apparatus 300 A and 300 b can be configured to perform 2D or 3D sensing based on the signal characteristics of the switch signal TG 1 and TG 2 .

Foregoing embodiments illustrate the photo-detecting apparatuses with either one-tap configuration or two-tap configuration. In some implementations, the tap number can be more than two. One may implement a 4-tap or more to configure a photo-detecting apparatus based on different design requirements.

Multi-Reset Mechanism

As the photo-detecting apparatus may be used in different environments, such as strong ambient light or weak ambient light, the dark current could be a factor to influence the stability. Below embodiments provide some solutions, using multi-reset mechanism, in which resetting the charge stored in the capacitor before the stored charge running-out so as to stabilize the photo-detecting apparatus.

FIG. 4A is a timing diagram showing an operation of a photo-detecting apparatus. It is noted that this timing diagram can be applied to any embodiment of the photo-detecting apparatus, including 2D or 3D sensing applications, disclosed in this application. As illustrated in FIG. 4A , the photo-detecting apparatus includes sleep mode, integration mode and data conversion mode. At very first begging, the photo-detecting apparatus is operated under sleep mode, there is no operation during this period. To obtain the depth or intensity information for each subframe, multi-reset mechanism is applied. In other words, the resetting times of the reset signal RST is equal to or greater than two during a formation of a subframe. Assuming its timing is applied when the reset signal RST is asserted in, e.g., the photo-detecting apparatus 200 A, the capacitors 150 A and 150 B will be charged to the voltage VDDR. Accordingly, the capacitors 150 A and 150 B will be discharged when the incident light IL comes in and the electrical signal IA 1 and IA 2 are generated. After an integration time (e.g., Tsf 11 ), the voltages VOUT 1 and VOUT 2 will respectively drop to a settled voltage, and then these two settled voltages can be respectively read out to the bit-lines BL-A and BL-B during data conversion period. In this embodiment, one subframe (e.g., Subframe 1 ) is obtained after four times (e.g., timings T 1 , T 3 , T 5 and T 7 ) reset signals RST. In other words, the depth or intensity information of each pixel of each subframe is obtained based on four settled voltages (e.g., the settled voltages at timings T 2 , T 4 , T 6 and T 8 ). After a plurality of subframes are obtained, a final 3D frame can be obtained according to these subframes (e.g., 20 subframes, 40 subframes, 60 subframes or other numbers of subframes). For example, the final 3D frame can be obtained according to an average of these subframes, an average of particular frames, or providing different weighting for each subframe. Similar calculation and approach can be applied to 2D sensing. Through these calculations over the subframes, the accuracy of the final 2D/3D frame can be increased. While this embodiment takes four reset signals RST as illustration, one may use two or more reset signals RST to obtain one subframe. On the other hands, this multi-reset mechanism can be used in one-tap, two-tap or more taps configurations. Furthermore, the reset frequency can be configured as fixed or dynamic according to the design requirements.

FIG. 4B illustrates a timing diagram for a photo-detecting apparatus used in 3D sensing application, which is used for sending image depth. As shown in FIG. 4B , switch signals TG 1 and TG 2 are demodulation signals. In this embodiment, demodulation signal (e.g. switch signal TG 1 or TG 2 ) is a continuous square wave signal during an integration operation. Specifically, the demodulation signal has phase offsets. In this embodiment, each switch signal TG 1 or TG 2 includes offsets of four phases (0-degree, 180-degree, 90-degree and 270-degree). Said the offsets of the four phases will be applied in turn. Taking switch signal TG 1 as an example, the switch signal TG 1 applies phase 0-degree during time period Tsf 11 , applies phase 180-degree during time period Tsf 12 , applies phase 90-degree during time period Tsf 13 , applies phase 270-degree during time period Tsf 14 and so forth. The switch signal TG 2 is a reversed signal of switch signal TG 1 . One may only use switch signal TG 1 if the photo-detecting apparatus is a one-tap configuration. Applying the phase-offset switch signal, the image depth information can be obtained with enhanced accuracy.

FIG. 4C illustrates a timing diagram for a photo-detecting apparatus used in 2D sensing application, which is used for sensing image intensity. As shown in FIG. 4C , switch signals TG 1 and TG 2 are the same and non-demodulation signals. In this embodiment, the switch signals TG 1 and TG 2 are turns-on signals for turning-on the switch 171 A and 171 B simultaneously during an integration operation so that the photo-detecting apparatus as in FIG. 2D-1 to FIG. 2D-4 can obtain the image intensity. In one implementation, one may only use switch signal TG 1 if the photo-detecting apparatus is a one-tap configuration as in FIG. 1J-1 to 1J-4 . In another implementation, one may use the switch signal TG 1 and disable the switch signal TG 2 if the photo-detecting apparatus as in FIG. 2D-1 to FIG. 2D-4 is a two-tap configuration.

In accordance with the foregoing embodiments, this application integrates the cascode transistor coupled between the reset transistor and the optical-to-electric converter, where the cascode transistor is capable of providing a low-level constant voltage at the output terminal of the optical-to-electric converter and being configured as a current buffer. With this configuration, the dark current generated by the optical-to-electric converter can be reduced and the signal-to-noise ratio is accordingly increased.

In some implementations, the optical-to-electric converter uses a light-absorption material formed on a semiconductor substrate, where the light-absorption material is different from the semiconductor substrate. For example, Ge-on-Si technology uses the light-absorption material Ge (1-x) Si x , wherein 0≤x<1, formed on the silicon semiconductor substrate to absorb the incident light. This technology is capable of absorbing the light having a longer NIR wavelength (e.g., the wavelength is greater than 940 nm, even more than 1100 nm) and therefore protect the human eyes.

Furthermore, using multi-reset mechanism in the photo-detecting apparatus can prevent from the charge run-out problem and increase the stability of the photo-detecting apparatus. In addition, the phase-offset switch signal is also introduced to obtain the image depth information with enhanced accuracy.

While the invention has been described by way of example and in terms of a preferred embodiment, it is to be understood that the invention is not limited thereto. On the contrary, it is intended to cover various modifications and similar arrangements and procedures, and the scope of the appended claims therefore should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements and procedures.

Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.