PHASE CHANGE MATERIAL-BASED DISPLAY DEVICE WITH RESISTIVE SWITCHING ELEMENTS

• US 20200133033A1
• Filed: 09/05/2017
• Published: 04/30/2020
• Est. Priority Date: 09/23/2016
• Status: Active Grant

• Current Assignee: E Ink Holdings Incorporated
• Original Assignee: Bodle Technologies Limited
• Inventors: BHASKARAN, Harish, HOSSEINI, Peiman, BROUGHTON, Ben
• Granted Patent: US 10,884,267 B2
• Time in Patent Office: Days
• CPC Class Codes: G02F 1/0121 Operation of devices; Circuit arrangements, not otherwise provided for in this subclass
• CPC Class Codes: G02F 1/0147 based on thermo-optic effects G02F1/132 takes precedence
• CPC Class Codes: G02F 1/1365 in which the switching element is a two-electrode device G02F1/136277 takes precedence
• CPC Class Codes: G09G 2300/06 Passive matrix structure, i.e. with direct application of both column and row voltages to the light emitting or modulating elements, other than LCD or OLED
• CPC Class Codes: G09G 2300/0885 Pixel comprising a non-linear two-terminal element alone in series with each display pixel element
• CPC Class Codes: H10B 63/20 comprising selection components having two electrodes, e.g. diodes
• CPC Class Codes: H10B 63/22 of the metal-insulator-metal type
• CPC Class Codes: H10B 63/24 of the Ovonic threshold switching type
• CPC Class Codes: H10N 70/231 based on solid-state phase change, e.g. between amorphous and crystalline phases, Ovshinsky effect
• CPC Class Codes: H10N 70/826 adapted for essentially vertical current flow, e.g. sandwich or pillar type devices
• CPC Class Codes: H10N 70/8613 Heating or cooling means other than resistive heating electrodes, e.g. heater in parallel
• CPC Class Codes: H10N 70/8822 Sulfides, e.g. CuS
• CPC Class Codes: H10N 70/8825 Selenides, e.g. GeSe
• CPC Class Codes: H10N 70/8828 Tellurides, e.g. GeSbTe
• CPC Class Codes: H10N 70/8833 Binary metal oxides, e.g. TaOx
• CPC Class Codes: H10N 70/884 Other compounds of groups 13-15, e.g. elemental or compound semiconductors

Abstract

The present invention is notably directed to display device (1, la d), comprising a set of pixels, each having a layer structure (2, 2c, 2d) that includes: a bi-stable, phase change material (10), or bi-stable PCM, having at least two reversibly switchable states, in which the PCM exhibits two different values of refractive index and/or optical absorption; and a heating element (17, 17c, 17d), electrically insulated from the PCM (10) and in thermal communication with the PCM (10) in the layer structure (2, 2c, 2d). The display device further comprises a set of nonlinear, monostable resistive switching elements (21), each in electrical communication with the heating element (17, 17c, 17d) of one of the pixels. The resistive switching elements are designed so as to exhibit, each: a low resistance, unstable state, which allows the heating element (17, 17c, 17d) to be energized via the resistive switching element (21), so as to heat the PCM (10) and reversibly change a refractive index and/or an optical absorption thereof, in operation; and a high-resistance, stable state, which allows leakage currents to be mitigated, so as to prevent inadvertent switching of the PCM (10) from one of its states to the other, in operation. The device further comprises a controller (30) configured to energize any of the pixels via a respective one of the resistive switching elements (21), so as to switch the latter from its high-resistance state to its low resistance state, in order to energize a respective heating element (17, 17c, 17d) and, in turn, reversibly change a refractive index and/or an optical absorption of a respective PCM (10). The present invention is further directed to related devices or apparatuses, such as passive matrix addressing displays, and methods of operations.

Claims

1. A display device, comprising:

a set of pixels, each having a layer structure that includes;

a bi-stable, phase change material, or bi-stable PCM, having at least two reversibly switchable states, in which the PCM exhibits two different values of refractive index and/or optical absorption; and

a heating element, electrically insulated from the PCM and in thermal communication with the PCM in the layer structure;

and wherein the display device further comprises;

a set of nonlinear, monostable resistive switching elements each in electrical communication with the heating element of one of the pixels, and designed so as to exhibit;

a low resistance, unstable state, which allows the heating element to be energized via the resistive switching element, so as to heat the PCM and reversibly change a refractive index and/or an optical absorption thereof, in operation; and

and a high-resistance, stable state, which allows leakage currents to be mitigated, so as to prevent inadvertent switching of the PCM from one of its states to the other, in operation; and

a controller configured to energize any of the pixels via a respective one of the resistive switching elements, so as to switch the latter from its high-resistance state to its low resistance state, in order to energize a respective heating element and, in turn, reversibly change a refractive index and/or an optical absorption of a respective PCM.

2. The display device according to claim 1, wherein:

the device is a passive matrix addressing display, which further comprises an arrangement of pairs of electrodes, each of the pairs of electrodes being in electrical communication with a heating element of one of the pixels, via a respective one of the resistive switching elements that is connected in series between the electrodes of said each of the pairs, so as for each of the pixels to be individually addressable by the controller in the display device.

3. The display device according to claim 2, wherein:

each of the pixels comprises said respective one of the resistive switching elements, the latter stacked in the layer structure of said each of the pixels.

4. The display device according to claim 3, wherein:

said arrangement of pairs of electrodes forms a matrix, whereby first electrodes of the pairs of electrodes are arranged in columns and second electrodes of the pairs of electrodes are arranged in rows; and

each of the pixels is offset, in a direction perpendicular to a stacking direction (z) of the layer structure of said each of the pixel, from a crosspoint formed at an intersection of one of the first electrodes with one of the second electrodes, said one of the first electrodes and said one of the second electrodes being in electrical communication with the resistive switching element of said each of the pixels.

5. The display device according to claim 2, wherein:

each of the pairs of electrodes is in electrical communication with the heating element of one of the through two vias extending, each, parallel to a stacking direction (z) of the layer structure of said one of the pixel, wherein one of said vias comprises the resistive switching elements that is in electrical communication with the heating element of said one of the pixels.

6. The display device according to claim 5, wherein:

said two vias both extend between an average plane of said arrangement of pairs of electrodes and an average plane of the heating element said one of the pixels, said heating element being preferably configured as an optical reflector.

7. The display device according to claim 5, wherein:

first electrodes of the pairs of electrodes extend in a first plane on one side of an average plane of the heating element of said one of the pixels, and

second electrodes of the pairs of electrodes extend in a second plane on another side of said average plane of the heating element, said second electrodes being preferably configured as optical reflectors,

and wherein,

one of said two vias is connected to one of said first electrodes, the other one of said two vias being connected to one of the second electrodes.

8. The display device according to claim 1, wherein the layer structure further comprises:

a thermally conducting, optical reflector;

a thermally conducting spacer, which is transmissive to light and arranged above the reflector,

wherein,

the PCM is arranged above the spacer, so as for the reflector, the spacer and the PCM to be successively stacked along a stacking direction (z) of the layer structure, and

the heating element is opposite to the PCM with respect to the reflector, the layer structure being configured so as for the heating element to be in thermal communication with the PCM via the reflector and the spacer.

9. The display device according to claim 8, wherein:

an average thickness of the reflector is between 50 nm and 1 μ

m;

an average thickness of the spacer is between 10 nm and 250 nm; and

an average thickness of the PCM is between 0.5 nm and 500 nm, and preferably between 1 nm and 100 nm, and more preferably between 7 nm and 15 nm.

10. The display device according to claim 1, wherein:

an average thickness of the heating element is between 20 nm and 2 μ

m, and preferably between 60 nm and 140 nm; and

an average thickness of the resistive switching element is between 10 nm and 100 nm, and preferably between 10 nm and 30 nm.

11. A display device according to claim 1, wherein:

each of the resistive switching elements is a threshold switching device, and preferably is one of;

an ovonic threshold switch;

a metal-insulator transition device;

a diode; and

a threshold vacuum switch.

12. A display device according to claim 1, wherein:

each of the resistive switching elements comprises a material that is one of;

an oxide;

a nitride;

a sulfide;

an oxynitride; and

diamond, said resistive switching element preferably comprising one or more materials that comprise, each, one or more of;

NbO_x, VO_x, HfO₂, SiO₂, ZrO₂, and TiO₂.

13. A display device according to claim 1, wherein the PCM comprises one or more of the following compounds:

GeSbTe, VO_x, NbO_x, GeTe, GeSb, GaSb, AgInSbTe, InSb, InSbTe, InSe, SbTe, TeGeSbS, AgSbSe, SbSe, GeSbMnSn, AgSbTe, AuSbTe, and AlSb.

14. A display device according to claim 1, wherein the heating element of each of the pixels comprises one or more of the following:

NiCrSi, NiCr, W, TiW, Pt, Ta, Mo, Nb and Ir.

15. A method for controlling a display device according to claim 1, the method comprising:

repeatedly energizing the pixels, via the controller, so as to reversibly switch resistive switching elements electrical communication with respective heating elements of the pixels and energize the respective heating elements to reversibly change a refractive index and/or an optical absorption of respective PCMs of the pixels.