# US 6,570,784 B2 · Programming a phase-change material memory > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 6,570,784 B2 - Document ID: US6570784B2 - Status: Granted - Kind: B2 - Application number: 09/895,135 - Filed: 2001-06-29 - Published: 2003-01-02 - Granted: 2003-05-27 - Earliest claimed: 2001-06-29 - Assignees: Ovonyx, Inc. - Inventors: Tyler A. Lowrey - Web page: https://patentgrep.com/patent/US6570784B2 ## CPC - G11C 13/0069: {Writing or programming circuits or methods} - G11C 11/5678: {using amorphous/crystalline phase transition storage elements} - G11C 13/0004: {comprising amorphous/crystalline phase transition cells} - G11C 2013/0092: {Write characterized by the shape, e.g. form, length, amplitude of the write pulse} - G11C: STATIC STORES (semiconductor memory devices H10B) ## Abstract The memory device has constituent cells which include a structural phase-change material to store the cells data. This material may be, for instance, a chalcogenide alloy. A first pulse is applied to the cell to leave the material in a first state, such as a reset state in which the material is relatively amorphous and has relatively high resistivity. Thereafter, a second pulse is applied to the cell to change the material from the first state to a second, different state, such as a set state in which the material is relatively crystalline and has relatively low resistivity. This second pulse has a generally triangular shape, rather than a rectangular one. ## Claims ### Claim 1 A method comprising: applying a signal to a first memory material; applying a second signal to the first memory material; and selecting a decay rate of the signal so that a fall time of the signal is greater than a fall time of the second signal. ### Claim 2 (depends on 1) The method of claim 1 including altering a resistance of the first memory material. ### Claim 3 (depends on 2) The method of claim 2, wherein the decay rate is set to alter the resistance of the memory material from a first resistance to a second resistance that is lower than the first resistance. ### Claim 4 (depends on 1) The method of claim 1 including altering a state of the memory material. ### Claim 5 (depends on 4) The method of claim 4, wherein the state is altered from a first state to a second state and a resistance of the memory material in the first state is greater than the resistance of the memory material in the second state. ### Claim 6 (depends on 4) The method of claim 4, further comprising applying the signal to a second memory material having different programming characteristics than the first memory material and wherein setting the decay rate of the signal includes setting the decay rate so that the memory material and the second memory material are placed in a predefined state when the signal is applied to the first and second memory materials. ### Claim 7 (depends on 6) The method of claim 6, wherein the different programming characteristics include variations in resulting resistance of the first and second memory materials when a rectangular pulse having a predetermined amount of current is applied to the first and second memory materials, wherein the variations are due to fabrication process and material variations. ### Claim 8 (depends on 4) The method of claim 4, wherein a magnitude of the signal is sufficient to heat the memory material to an amorphizing temperature when the signal is applied to the memory material and wherein the decay rate is set so that after the memory material reaches the amorphizing temperature, the memory material cool downs at a sufficient rate so that the memory material is placed in a first state from a second state. ### Claim 9 (depends on 1) The method of claim 1, wherein the signal places the memory material in a first state when the signal is applied to the memory material and the second signal places the memory material in a second state when the second signal is applied to the memory material. ### Claim 10 (depends on 9) The method of claim 9, wherein the first state is a crystalline state and the second state is a amorphous state. ### Claim 11 (depends on 9) The method of claim 9, wherein a resistance of the memory material in the first state is less than the resistance of the memory material in the second state. ### Claim 12 (depends on 1) The method of claim 1, wherein the signal is a pulse having a leading portion and a trailing portion, wherein the leading portion occurs prior to the signal reaching a maximum level and the trailing portion occurs after the signal reaches the maximum level. ### Claim 13 (depends on 12) The method of claim 12, further comprising setting the decay rate of the signal by setting a slope of the trailing portion of the signal. ### Claim 14 (depends on 1) The method of claim 1, wherein the memory material is a phase-change material. ### Claim 15 A method comprising: applying a signal to a first memory material; and setting a slope of a trailing portion of the signal to set a fall time of the signal to place the memory material in a selected state. ### Claim 16 (depends on 15) The method of claim 15, wherein the signal is a pulse having a leading portion and the trailing portion, wherein the leading portion occurs prior to the signal reaching a maximum level and the trailing portion occurs after the signal reaches the maximum level. ### Claim 17 (depends on 15) The method of claim 15, wherein setting the slope includes applying a slope that varies with time. ### Claim 18 (depends on 15) The method of claim 15, wherein the slope is set to increase with time. ### Claim 19 (depends on 15) The method of claim 15, wherein the slope is set to a nonlinear slope. ### Claim 20 (depends on 15) The method of claim 15, wherein setting the slope comprises shaping the trailing portion to change from a negative slope to a substantially vertical slope. ### Claim 21 (depends on 15) The method of claim 15, wherein setting the slope comprises shaping the signal so that the signal is nonrectangular. ### Claim 22 (depends on 15) The method of claim 15, further comprising applying a second signal to the memory material, wherein the slope of the trailing portion of the signal is set so that the slope of the trailing portion of the signal is different than a slope of a trailing portion of the second signal. ### Claim 23 (depends on 22) The method of claim 22, wherein the slope of the trailing portion of the second signal is substantially vertical and the slope of the trailing portion of the signal is negative. ### Claim 24 (depends on 15) The method of claim 15, wherein setting the fall time includes setting a decay rate of the signal. ### Claim 25 (depends on 15) The method of claim 15, wherein the memory material is a phase-change material. ### Claim 26 (depends on 15) The method of claim 15, further comprising applying a second signal to the memory material, wherein setting the fall time includes setting the fall time to be greater than a fall time of the second signal. ### Claim 27 (depends on 26) The method of claim 26, wherein a fall time of the second signal is substantially zero. ### Claim 28 (depends on 26) The method of claim 26, wherein the second signal places the memory material in a second state when the second signal is applied to the memory material. ### Claim 29 (depends on 28) The method of claim 28, wherein the selected state is a crystalline state and the second state is an amorphous state. ### Claim 30 (depends on 28) The method of claim 28, wherein a resistance of the memory material in the second state is greater than the resistance of the memory material in the selected state. ### Claim 31 (depends on 15) The method of claim 15, further comprising applying the signal to a second memory material having different programming characteristics than the first memory material and wherein setting a fall time of the signal includes setting a decay rate of the signal so that the memory material and the second memory material are placed in the selected state when the signal is applied to the first and second memory materials. ### Claim 32 (depends on 31) The method of claim 31, wherein the different programming characteristics include variations in resulting resistance of the first and second memory materials when a rectangular pulse having a predetermined amplitude is applied to the first and second memory materials, wherein the variations are due to fabrication process and material variations. ### Claim 33 (depends on 15) The method of claim 15, wherein a magnitude of the signal is sufficient to heat the memory material to an amorphizing temperature when the signal is applied to the memory material and wherein the fall time is set so that after the memory material reaches the amorphizing temperature, the memory material cool downs at a sufficient rate so that the memory material is placed in the selected state. ### Claim 34 (depends on 15) The method of claim 15, wherein the fall time is set to heat the memory material to a predetermined temperature to place the memory material in the selected state. ### Claim 35 A system, comprising: a processor; an input/output (I/O) device coupled to the processor; a memory comprising a phase change material and coupled to the processor; and a circuit adapted to provide at least two signals to apply to the memory to change a state of the memory, wherein the circuit sets fall time of the first and second signals so that the fall time of the first signal is less than the fall time of the second signal. ### Claim 36 (depends on 35) The system of claim 35, wherein the circuit comprises a waveshaping circuit to set the fall time of the second signal by shaping a slope of a trailing portion of the second signal. ### Claim 37 (depends on 36) The system of claim 36, wherein the slope is shaped to vary with time. ### Claim 38 (depends on 35) The system of claim 35, wherein the circuit comprises a waveshaping circuit to set the fall time of the second signal by setting a decay rate of the second signal. ### Claim 39 (depends on 35) The system of claim 35, wherein the circuit comprises a waveshaping circuit to set the fall time of the second signal by shaping the second signal to have a triangular shape. ### Claim 40 (depends on 35) The system of claim 35, wherein the predefined state is a crystalline state. ### Claim 41 (depends on 35) The system of claim 35, wherein the fall times of the first and second signals are set so as to place the phase change material of the memory in a first state when the first signal is applied to the phase change material and place the phase change material in a second state when the second signal is applied to the phase change material. ### Claim 42 (depends on 41) The system of claim 41, wherein a resistance of the phase change material in the second state is lower than the resistance of the phase change material in the first state. ### Claim 43 A method comprising: applying a first signal to a first memory material; applying the signal to a second memory material having different programming characteristics than the first memory material; and setting the decay rate of the signal by setting the decay rate so that the memory material and the second memory material are placed in a predefined state when the signal is applied to the first and second memory materials. ### Claim 44 (depends on 43) The method of claim 43 wherein the different programming characteristics include variations in resulting resistance of the first and second memory materials when a rectangular pulse having a predetermined amount of current is applied to the first and second memory materials. ### Claim 45 A method comprising: applying a signal to a memory material; setting a decay rate of the signal to alter a characteristic of the memory material; and setting the magnitude of the signal at a level sufficient to heat the memory material to an amorphizing temperature when the signal is applied to the memory material and wherein the decay rate is set so that after the memory material reaches the amorphizing temperature, the memory material cools down at a sufficient rate so that the memory material is placed in a first state from a second state. ### Claim 46 A method comprising: applying a signal to a memory material; setting a fall time of the signal to place the memory material in a selective state; and applying the signal to a second memory material having different programming characteristics than the first memory material and wherein setting a fall time of the signal includes setting a decay rate of the signal so that the memory material and the second memory material are placed in the selective state when the signal is applied to the first or second memory materials. ### Claim 47 (depends on 46) The method of claim 46, wherein the different programming characteristics include variations in resulting resistance of the first and second memory materials when a rectangular pulse having a predetermined amplitude is applied to the first and second memory materials. ### Claim 48 A method comprising: applying a signal to a memory material; setting a fall time of the signal to place the memory material in a selected state; and setting a magnitude of the signal at a level sufficient to heat the memory material to a amorphizing temperature when the signal is applied to the memory material and wherein the fall time is set so that after the memory material reaches the amorphizing temperature, the memory material cools down at a sufficient rate so that the memory material is placed in the selected state. ### Claim 49 A method comprising: applying a signal to a memory material; setting a fall time of the signal to place the material in a selective state; and applying a second signal to the memory material, wherein setting the fall time includes setting the fall time to be greater than a fall time of the second signal. ### Claim 50 (depends on 49) The method of claim 49 wherein a fall time of the second signal is substantially zero. ### Claim 51 (depends on 49) The method of claim 49 wherein the second signal places the memory material in a second state when the second signal is applied to the memory material. ### Claim 52 (depends on 51) The method of claim 51 wherein the selective state is a crystalline state and the second state is an amorphous state. ### Claim 53 (depends on 51) The method of claim 51 wherein a resistance of the memory material in the second state is greater than the resistance of the material in a selective state. ### Claim 54 A method comprising: applying a signal to a memory material; setting a fall time of the signal to place the memory material in a selective state; and making the magnitude of signal sufficient to heat the memory material to an amorphizing temperature when the signal is applied to the memory material and wherein the fall time is set so that after the memory material reaches the amorphizing temperature, the memory material cools down at a sufficient rate so that the memory material is placed in a selective state. ### Claim 55 A method comprising: applying a first signal to a plurality of cells having a memory material; and applying a second signal to the memory material of said cells so that all of the cells pass through the rapid crystallization temperature interval. ### Claim 56 (depends on 55) The method of claim 55 wherein the decay rate of the second signal is such that the fall time of the second signal is greater than the fall time of the first signal. ### Claim 57 (depends on 55) The method of claim 55 wherein the second signal is triangular. ### Claim 58 (depends on 57) The method of claim 57 wherein the second signal has a linear fall time. ### Claim 59 (depends on 57) The method of claim 57 wherein the second signal has a non-linear fall time. ### Claim 60 (depends on 57) The method of claim 57 wherein said second signal has a substantially linear region and a substantially non-linear region.