Memory device and operation method thereof

The disclosure relates in general to a memory device having CIM (Computing in Memory) function and an operation method thereof.

CIM (Computing in Memory) may be used in AI (Artificial intelligence) accelerator structure. Data operations are performed in the CIM memory device and the operation results are output to the processor. Thus, by comparison, CIM may have advantages, such as, lowered power consumption, improved operation efficiency, and thus is suitable in implementing AI in user terminal.

In order to further reduce power consumption and improve integrability, resistive switches are used to implement logic operation units having CIM function. Different voltages are applied to switch the logic operation function of the logic operation unit. However, multi-voltage operation structure will increase processing procedure complexity and peripheral circuit complexity.

According to one embodiment, a memory device is provided. The memory device comprises: a memory array including a plurality of memory cells; a plurality of bit lines coupled to the memory array; a plurality of word lines coupled to the memory array; and a plurality of conductance controllable units coupled to the memory array; wherein a memory cell group and at least one conductance controllable unit among the conductance controllable units form a logic operation unit, and a logic operation function of the logic operation unit is determined by an equivalent conductance of the at least one conductance controllable unit.

According to another embodiment, provided is an operation method for a memory device, the operation method comprising: selecting a memory cell group of a plurality of memory cells of the memory device and at least one conductance controllable unit to form a logic operation unit; and controlling an equivalent conductance of the at least one conductance controllable unit to determine a logic operation function of the logic operation unit.

FIG. 1A and FIG. 1B show two kinds of circuit structures of the logic operation units of a memory device according to two embodiments of the application.

FIG. 2 shows voltage-current characteristic figure of the resistive switch according to one embodiment of the application.

FIG. 3A to FIG. 3E show several possible embodiments of the conductance controllable unit.

FIG. 4 shows a voltage waveform according to one embodiment of the application.

FIG. 5 shows a circuit structure of the logic operation unit of the memory device according to one embodiment of the application.

FIG. 6 shows signal waveform in performing NOR operation.

FIG. 7A shows circuit diagram of the logic operation unit for executing the logic operations Y=(ĀB+A B )S; FIG. 7B shows the logic gates for executing the logic operations Y=(ĀB+A B )S; and FIG. 7C shows the signal waveform for executing the logic operations Y=(ĀB+A B )S.

FIG. 8A to FIG. 8G show circuit diagrams of a memory device according to several embodiments of the application.

In the following detailed description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the disclosed embodiments. It will be apparent, however, that one or more embodiments may be practiced without these specific details. In other instances, well-known structures and devices are schematically shown in order to simplify the drawing.

Technical terms of the disclosure are based on general definition in the technical field of the disclosure. If the disclosure describes or explains one or some terms, definition of the terms is based on the description or explanation of the disclosure. Each of the disclosed embodiments has one or more technical features. In possible implementation, one skilled person in the art would selectively implement part or all technical features of any embodiment of the disclosure or selectively combine part or all technical features of the embodiments of the disclosure.

Now refer to FIG. 1A and FIG. 1B , which show two kinds of circuit structures of the logic operation units of a memory device according to two embodiments of the application.

In FIG. 1A , the logic operation unit 100 A includes: resistive switches A, B and Y, and a conductance controllable unit C.

The resistive switches A, B and Y are parallel. The resistive switch A includes one terminal coupled to a word line WL 1 and another terminal coupled to a bit line BL. The resistive switch B includes one terminal coupled to a word line WL 2 and another terminal coupled to the bit line BL. The resistive switch Y includes one terminal coupled to a word line WL 3 and another terminal coupled to the bit line BL. The conductance controllable unit C includes one terminal coupled to the bit line BL and another terminal coupled to ground.

In FIG. 1B , the logic operation unit 100 B includes: resistive switches A, B and Y, a conductance controllable unit C and an access transistor Taccess. The access transistor Taccess is optional in embodiments of the application.

The access transistor Taccess includes one terminal (for example, a drain terminal) coupled to the bit line BL, another terminal (for example, a source terminal) coupled to a sensing amplifier (not shown) and a control terminal (for example, a gate terminal) for receiving a gate control voltage (not shown). The access transistor Taccess provides a reading current or a reading voltage, to read or change the conductance state of the resistive switches.

In embodiments of the application, as shown in FIG. 1A and FIG. 1B , via changing an equivalent conductance of the conductance controllable unit C, the operation functions of the logic operation units 100 A and 100 B are controlled. Here, the operation functions of the logic operation units 100 A and 100 B include, for example but not limited by, NAND logic operations and NOR logic operations.

In one embodiment of the application, when the conductance controllable unit C has a first equivalent conductance, the operation functions of the logic operation units 100 A and 100 B are controlled as NAND logic operations; and when the conductance controllable unit C has a second equivalent conductance, the operation functions of the logic operation units 100 A and 100 B are controlled as NOR logic operations. The first equivalent conductance is higher than the second equivalent conductance. For example but not limited by, the first equivalent conductance is double of the second equivalent conductance.

In one embodiment of the application, the resistive switches A and B also refer as the input cells for storing input data before logic operations; and the resistive switch Y also refers as the output cell(s) for storing output data obtained after logic operations.

Further, the resistive switches A, B and the conductance controllable unit C form a voltage divider which determines the bit line voltage Vint on the bit line BL and determines the final stage of the resistive switch Y. Details are as below.

FIG. 2 shows voltage-current characteristic figure of the resistive switch according to one embodiment of the application. As shown in FIG. 2 , when the voltage drop of the resistive switch exceeds a set voltage VSET, the resistive switch is programmed (changed) from a high resistance state (HRS) into a low resistance state (LRS). On the contrary, when the reverse voltage drop of the resistive switch exceeds a reset voltage, the resistive switch is programmed (changed) from the LRS to the HRS.

In one embodiment of the application, the LRS state and the HRS stage of the resistive switch is, for example but not limited by, defined as logic 1 and logic 0, respective. G HRS and G LRS refer to the conductance value of the resistive switch as the HRS and LRS, respectively, wherein G HRS <<G LRS .

In FIG. 1A and FIG. 1B , the input voltage Vi is applied to the word lines WL 1 and WL 2 . That is, the input voltage Vi is applied to the resistive switches A and B. The output voltage Vo is applied to the word line WL 3 . That is, the output voltage Vo is applied to the resistive switch Y. Still further, the resistive switch Y has an initial state of HRS.

By voltage division rule, the bit line voltage Vint is expressed as below.

When the resistive switches A and B are both at LRS, the bit line voltage Vint is expressed as: Vint=Vi*(G LRS )/(G LRS +0.5 G L ), wherein “G L ” refer to the conductance value of the conductance controllable unit C.

When one among the resistive switches A and B is at LRS while the other one among the resistive switches A and B is at HRS, the bit line voltage Vint is expressed as: Vint=Vi*(G LRS )/(G LRS +G L ).

When the resistive switches A and B are both at HRS, the bit line voltage Vint is expressed as: Vint=0V.

When the resistive switch Y is to be programmed, the voltage drop of the resistive switch Y is to be higher than the set voltage VSET. In other words, when a difference vale (Vo−VSET) between the output voltage Vo and the set voltage VSET is higher than the bit line voltage Vint, the resistive switch Y is programmed (from HRS into LRS).

Nand Logic Operations

In one embodiment of the application, in the case that the difference vale (Vo−VSET) between the output voltage Vo and the set voltage VSET is between “Vi*(Gus)/(G LRS +0.5G L )” and “Vi*(G LRS )/(G LRS +G L )”, then (1) when at least one among the resistive switches A and B is at HRS, the resistive switch Y is programmed into LRS (Y=0); (2) when the resistive switches A and B are both at LRS, the resistive switch Y is not programmed (the resistive switch Y is at HRS, and Y=1).

In other words, in this case, the logic states of the resistive switches A, B and Y are as below:

Thus, in this case, the operation function of the logic operation units 100 A and 100 B is NAND logic operations.

Nor Logic Operations

In one embodiment of the application, in the case that the difference vale (Vo-VSET) between the output voltage Vo and the set voltage VSET is between “Vi*(G LRS )/(G LRS +G L )” and “0V”, then (1) when the resistive switches A and B are both at HRS, the resistive switch Y is programmed into LRS (Y=0); (2) when one among the resistive switches A and B is at HRS and the other one among the resistive switches A and B is at LRS, the resistive switch Y is not programmed (the resistive switch Y is at HRS, and Y=1); and (3) when the resistive switches A and B are both at LRS, the resistive switch Y is not programmed (the resistive switch Y is at HRS, and Y=1).

In other words, in this case, the logic states of the resistive switches A, B and Y are as below:

Thus, in this case, the operation function of the logic operation units 100 A and 100 B is NOR logic operations.

Still further, in order to make a maximum gap between “Vi*(G LRS )/(G LRS +0.5G L )” and “Vi*(G LRS )/(G LRS +G L )” for better operation results, the conductance value “G L ” of the conductance controllable unit C is set as G L =√{square root over (2)}G LRS , but the application is not limited by this. The conductance value “G L ” of the conductance controllable unit C may be set as other proper values.

Thus, in one embodiment of the application, when G L =√{square root over (2)}G LRS (G L is set as a preferred value), the voltage difference (Vo−VSET) is expressed as Vo−VSET=(½)*Vi, but the application is not limited by. When at least one among the resistive switches A and B is at HRS, the resistive switch Y is programmed, in other words, the logic operation units 100 A and 100 B has NAND logic operation function.

In case that the conductance value “G L ” of the conductance controllable unit C is set as a half of the preferred value (G L =(1/√{square root over (2)})*G LRS ), when the resistive switches A and B are both as HRS, the resistive switch Y is programmed, in other words, the logic operation units 100 A and 100 B has NOR logic operation function.

Thus, in one embodiment of the application, via controlling the conductance value “G L ” of the conductance controllable unit C, the logic operation units 100 A and 100 B are switched between NAND logic operation and NOR logic operation.

Now refer to FIG. 3A to FIG. 3E , which show several possible embodiments of the conductance controllable unit C.

In FIG. 3A , the conductance controllable unit C includes a transistor T 1 . In FIG. 3A , the transistor T 1 is at the linear region to adjust the equivalent conductance of the conductance controllable unit C. Higher the gate voltage applied to the gate of the transistor T 1 , lower the equivalent conductance of the conductance controllable unit C; and vice versa.

In FIG. 3B , the conductance controllable unit C includes a floating-gate transistor T 2 and a transistor T 3 . In FIG. 3B , the transistor T 3 provides a drain current to program or erase the floating-gate transistor T 2 , for changing the equivalent conductance value of the floating-gate transistor T 2 at the linear region. During logic operation, the transistor T 3 is turned off.

In FIG. 3C , the conductance controllable unit C includes a resistive switch RW and a transistor T 4 . The transistor T 4 provides a voltage or a current to control the conductance of the resistive switch TW. Similarly, during the logic operation, the transistor T 4 is turned off.

In FIG. 3D , the conductance controllable unit C includes a multi-terminal transistor T 5 , wherein one terminal of the multi-terminal transistor T 5 is not necessary to be grounded.

In FIG. 3E , the conductance controllable unit C includes a resistive switch RW and a cascaded selector S. In one embodiment of the application, the selector S may be implemented by a unipolar diode, a bipolar diode, an OTS, a metal-insulator-metal film (the insulator may be Al 2 O 3 , a transition metal oxide and so on), a metal-insulator-transition material (VOx, NbOx and so on).

From FIG. 3A to FIG. 3E , in one embodiment of the application, the conductance controllable unit C may be volatile or non-volatile. The conductance controllable unit C may be a single transistor, a floating-gate transistor, a Ferroelectric RAM (FeRAM or FRAM).

Further, in one possible embodiment of the application, the conductance controllable unit C may be a two-terminal element or a multi-terminal element having one terminal not necessary to be grounded.

FIG. 4 shows a voltage waveform according to one embodiment of the application. In FIG. 4 , “Vread” refer to the read voltage applied to the word lines WL 1 to WL 3 in reading the resistive switch Y. The pulse width of the input voltage Vi is large enough to charge the bit line BL while the output voltage Vo is applied within the time duration of the input voltage Vi. The read voltage Vread and the input voltage Vi are small enough to prevent the resistive switches A, B and Y from altering its state.

In one possible embodiment of the application, the set voltage VSET may be within 0.5V to 3V; the input voltage Vi may be within 0.1V to 2V; the output voltage Vo may be within 0.3V to 5V; and the read voltage Vread may be within 0.02V to 1V. This is for example but not to limit the application.

FIG. 5 shows a circuit structure of the logic operation unit of the memory device according to one embodiment of the application. In FIG. 5 , the logic operation unit further including transistors T A , T B and T Y . The transistor T A is coupled between the word line WL 1 and the resistive switch A. The transistor T B is coupled between the word line WL 2 and the resistive switch B. The transistor T Y is coupled between the word line WL 3 and the resistive switch Y. The conductance controllable unit C is implemented by a transistor Tc.

In below, an example for performing NOR logic operation on logic states of the resistive switches A and B (Y=NOR(A,B)) is described, wherein A=1 and B=0.

FIG. 6 shows signal waveform in performing NOR operation.

In FIG. 6 , during the phase P 1 , the transistor T A is conducted while high level voltage is applied on the word line WL 1 to program the resistive switch A (A=1); the transistor T B is disconnected to prevent programming the resistive switch B (B=0); and the transistor T Y is disconnected but the access transistor Taccess is conducted to charge the bit line BL.

In the phase P 2 , the transistors T A , T B and T Y are conducted, the high-level voltages are applied to the word lines WL 1 to WL 3 and the initial conductance of the conductance controllable unit C is set as low conductance for performing NOR logic operation. Further, in the phase P 2 , the resistive switch Y is Y=NOR(A, B)=NOR(1, 0)=0.

In the phase P 3 , the resistive switch Y is read. Thus, during the phase P 3 , the transistors T A and T B are disconnected while the transistors T Y and Taccess are conducted; the conductance of the conductance controllable unit C is set as high conductance G L (G L >>G HRS ); and a small read voltage is applied to the word line WL 3 to read the current via the transistor Taccess and to read out the logic state of the resistive switch Y.

In one embodiment of the application, the logic operation units may be extended by adding more resistive switches for executing user-defined logic operation. In here, the logic operation Y=(ĀB+A B )S is as an example but the application is not limited by this.

FIG. 7A shows circuit diagram of the logic operation unit for executing the logic operations Y=(ĀB+A B )S; FIG. 7B shows the logic gates for executing the logic operations Y=(ĀB+A B )S; and FIG. 7C shows the signal waveform for executing the logic operations Y=(ĀB+A B )S. For executing the logic operations Y=(ĀB+A B )S, the operations may include three steps. In the first step, the logic operation Y1=NOR(A, B) is performed. In the second step, the logic operation Y2=NOR(Y1, S) is performed. In the third step, the logic operation Y=NAND(Y1, Y2) is performed. In FIG. 7A , S, Y1 and Y2 are resistive switches.

In the phase P 4 , the transistors T A , T B and T Y are conducted; high level voltages are applied to the word lines WL 1 , WL 2 and WL 4 and the conductance of the conductance controllable unit C is set as low conductance for performing NOR logic operation Y1=NOR(A, B).

In the phase P 5 , the transistors T Y1 , T Y2 and T s are conducted; high level voltages are applied to the word lines WL 3 , WL 4 and WL 5 ; and the conductance of the conductance controllable unit C is set as low conductance for performing NOR logic operation Y2=NOR(Y1, S).

In the phase P 6 , the transistors T Y1 , T Y2 and T Y are conducted; high level voltages are applied to the word lines WL 4 , WL 5 and WL 6 ; and the conductance of the conductance controllable unit C is set as high conductance for performing NAND logic operation Y=NAND(Y1, Y2).

By the above description, the embodiment may combine the required logic operation units to execute the user-defined logic operations.

Refer to FIG. 8A to FIG. 8G which show circuit diagrams of a memory device according to several embodiments of the application.

As shown in FIG. 8A , the memory device 800 A includes a memory array 810 , a plurality of bit lines BL 1 ˜BLN (N being a positive integer), a plurality of word lines WL 1 ˜WLM (M being a positive integer) and at least one conductance controllable unit C. The memory array 810 is coupled to the bit lines BL 1 ˜BLN, the word lines WL 1 ˜WLM and the at least one conductance controllable unit C. The memory array 810 includes a plurality of memory cells 820 , wherein the memory cells 820 may be implemented by the resistive switches (for example but not limited by, the resistive switches A, B and Y) in the above embodiments. That is, a memory cell group (for example but not limited by, the resistive switches A, B and Y) of the memory cells 820 and the at least one conductance controllable unit C form a logic operation unit. Or, in other possible embodiment of the application, each of the memory cells 820 may be implemented by a serial connection of the resistive switches (A, B and Y) and a selector/a transistor. In FIG. 8A , a plurality of control lines (not shown) for controlling the selector and/or the transistor of the memory cells 820 are parallel to the bit lines BL 1 ˜BLN or parallel to the word lines WL 1 ˜WLM, to form a semi-crossbar array.

As shown in FIG. 8B , the memory device 800 B includes the memory array 810 , the bit lines BL 1 ˜BLN, the word lines WL 1 ˜WLM and the at least one conductance controllable unit C. In FIG. 8B , the conductance values of the conductance controllable units C are controlled by a single conductance control line GCL for synchronically tuning the conductance values of the conductance controllable units C; and the conductance control line GCL is parallel to the bit lines BL 1 ˜BLN or parallel to the word lines WL 1 ˜WLM, to form a semi-crossbar array.

As shown in FIG. 8C , the memory device 800 C includes the memory array 810 , the bit lines BL 1 ˜BLN, the word lines WL 1 ˜WLM and the at least one conductance controllable unit C. In FIG. 8C , the conductance control lines GCL 1 ˜GCLP (P being a positive integer) for controlling the conductance values of the conductance controllable units C are independent (i.e. not coupled together) for independent tuning the conductance of the conductance controllable units C; and the conductance control lines GCL 1 ˜GCLP are parallel to the bit lines BL 1 ˜BLN or parallel to the word lines WL 1 ˜WLM, to form a semi-crossbar array.

As shown in FIG. 8D , the memory device 800 D includes the memory array 810 , the bit lines BL 1 ˜BLN, the word lines WL 1 ˜WLM and the at least one conductance controllable unit C. In FIG. 8D , the conductance values of the conductance controllable units C are controlled by the conductance control line GCL for synchronically tuning the conductance values of the conductance controllable units C; and the conductance control line GCL is parallel to the bit lines BL 1 ˜BLN or parallel to the word lines WL 1 ˜WLM, to form a semi-crossbar array. Further, the memory device 800 D further includes a conductance word line GWL coupled to the drains of the transistors of the conductance controllable units C; and the conductance word line GWL is parallel to the bit lines BL 1 ˜BLN or parallel to the word lines WL 1 ˜WLM.

As shown in FIG. 8E , the memory device 800 E includes the memory array 810 , the bit lines BL 1 ˜BLN, the word lines WL 1 ˜WLM and the at least one conductance controllable unit C. In FIG. 8E , the conductance control lines GCL 1 ˜GCLP (P being a positive integer) for controlling the conductance values of the conductance controllable units C are independent (i.e. not coupled together) for independent tuning the conductance of the conductance controllable units C; and the conductance control lines GCL 1 ˜GCLP are parallel to the bit lines BL 1 ˜BLN or parallel to the word lines WL 1 ˜WLM, to form a semi-crossbar array. Further, the memory device 800 E further includes a conductance word line GWL coupled to the drains of the transistors of the conductance controllable units C; and the conductance word line GWL is parallel to the bit lines BL 1 ˜BLN or parallel to the word lines WL 1 ˜WLM.

As shown in FIG. 8F , the memory device 800 F includes the memory array 810 , the bit lines BL 1 ˜BLN, the word lines WL 1 ˜WLM and the at least one conductance controllable unit C. In FIG. 8F , the conductance values of the conductance controllable units C are controlled by the conductance control line GCL for synchronically tuning the conductance values of the conductance controllable units C; and the conductance control line GCL is parallel to the bit lines BL 1 ˜BLN or parallel to the word lines WL 1 ˜WLM, to form a semi-crossbar array. Further, the memory device 800 F further includes a conductance word line GWL coupled to the drains of the transistors of the conductance controllable units C; and the conductance word line GWL is parallel to the bit lines BL 1 ˜BLN or parallel to the word lines WL 1 ˜WLM. Further, the memory device 800 F further includes a conductance tuning line GTL coupled to the gates of the floating-gate transistors of the conductance controllable units C; and the conductance tuning line GTL is parallel to the bit lines BL 1 ˜BLN or parallel to the word lines WL 1 ˜WLM.

As shown in FIG. 8G , the memory device 800 G includes the memory array 810 , the bit lines BL 1 ˜BLN, the word lines WL 1 ˜WLM and the at least one conductance controllable unit C. In FIG. 8G , the conductance values of the conductance controllable units C are controlled by the conductance control lines GCL 1 ˜GCLP for independently tuning the conductance values of the conductance controllable units C: and the conductance control lines GCL 1 ˜GCLP are parallel to the bit lines BL 1 ˜BLN or parallel to the word lines WL 1 ˜WLM, to form a semi-crossbar array. Further, the memory device 800 F further includes a plurality of conductance tuning lines GTL 1 ˜GTLP coupled to the gates of the floating-gate transistors of the conductance controllable units C; and the conductance tuning lines GTL 1 ˜GTLP are parallel to the bit lines BL 1 ˜BLN or parallel to the word lines WL 1 ˜WLM. Further, the memory device 800 G further includes a conductance word line GWL coupled to the drains of the transistors of the conductance controllable units C; and the conductance word line GWL is parallel to the bit lines BL 1 ˜BLN or parallel to the word lines WL 1 ˜WLM.

In one possible embodiment of the application, the resistive switch may be implemented by resistive random-access memory (RRAM including Metal Oxide Resistive Memory (OxRAM), conductive-bridging RAM (CBRAM) and so on), phase change memory (PCM), spin-transfer Torque MRAM (STT-MRAM), spin-orbit Torque MRAM (SOT-RAM), which are still within the spirit and scope of the application.

In one possible embodiment of the application, the CIM (Computing in Memory) logic operation units may be repeatedly arranged for expanding into a large scale array. Further, the array may be two-dimension or three-dimension structure. Detail operations of the expanded array may depend on customer requirements, resistive switches (optionally including the cascading selectors or transistors) and the types of the circuit (crossbar array or semi-crossbar array), which are still within the spirit and scope of the application.

The above embodiments of the application disclose a CIM memory device and the operation thereof which uses the resistive switches as the memory cells. The logic operation functions (for example, NAND and NOR) are switched by controlling the conductance value(s) of the conductance controllable unit(s). Thus, the embodiments of the application have advantages of simplifying the calculation complexity and the peripheral circuit complexity.

It will be apparent to those skilled in the art that various modifications and variations can be made to the disclosed embodiments. It is intended that the specification and examples be considered as exemplary only, with a true scope of the disclosure being indicated by the following claims and their equivalents.