OPTICAL DEVICE WITH THERMALLY SWITCHING PHASE CHANGE MATERIAL

• US 20190064555A1
• Filed: 01/25/2017
• Published: 02/28/2019
• Est. Priority Date: 02/04/2016
• Status: Active Grant

• Current Assignee: E Ink Corporation (E Ink Holdings Incorporated)
• Original Assignee: Bodle Technologies Limited
• Inventors: HOSSEINI, Peiman, BHASKARAN, Harish, BROUGHTON, Ben
• Granted Patent: US 11,215,852 B2
• Time in Patent Office: Days
• CPC Class Codes: G02F 1/0147 based on thermo-optic effects G02F1/132 takes precedence
• CPC Class Codes: G02F 2203/055 wavelength filtering
• CPC Class Codes: G02F 2203/34 Colour display without the use of colour mosaic filters
• CPC Class Codes: H01L 23/345 Arrangements for heating thermal treatment apparatus H01L21/00
• CPC Class Codes: H01L 27/1255 integrated with passive devices, e.g. auxiliary capacitors

Abstract

The present invention is notably directed to an optical device (1) comprising a layer structure (2) with: a thermally conducting, optical reflector (15); a thermally conducting spacer (14), which is transmissive to light and arranged above the reflector (15); and a phase change material (10), or PCM, arranged above the spacer (14) and having at least two reversibly switchable states, in which the PCM exhibits two different values of refractive index. The reflector (15), the spacer (14) and the PCM (10) are successively stacked along a stacking direction (z) of the layer structure. The optical device further comprises: a heating element (17), opposite to the PCM (10) with respect to the reflector (15), the layer structure (2) being configured so as to electrically insulate the PCM (10) from the heating element (17), while the heating element (17) is in thermal communication with the PCM (10) via the reflector (15) and the spacer (14); and a controller (19, 19a) configured to energize the heating element (17), so as to heat the PCM (10) and thereby reversibly change a refractive index and/or an absorption of said PCM (10). The invention is further directed to related optical devices (notably devices comprising one or more pixels formed, each, by a set of layer structures such as described above) and actuation methods.

Claims

1. An optical device comprising a layer structure with:

a thermally conducting, optical reflector;

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

a phase change material, or PCM, arranged above the spacer and having at least two reversibly switchable states, in which the PCM exhibits two different values of refractive index,

wherein,

the reflector, the spacer and the PCM are successively stacked along a stacking direction of the layer structure,

and wherein the optical device further comprises;

a heating element, opposite to the PCM with respect to the reflector, the layer structure being configured so as to electrically insulate the PCM from the heating element, while the heating element is in thermal communication with the PCM via the reflector and the spacer; and

a controller configured to energize the heating element, so as to heat the PCM and thereby reversibly change a refractive index and/or an absorption of said PCM.

2. The optical device of claim 1, wherein:

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

m;

an average thickness of the spacer is between 40 nm and 300 nm; and

an average thickness of the PCM is between 0.5 nm and 80 nm.

3. A device according to claim 1, wherein

a lateral dimension of the layer structure, perpendicularly to said stacking direction is greater than or equal to 0.35 μ

m and, preferably, greater than or equal to 5 μ

m.

4. A device according to claim 1, further comprising;

an electrically insulating material between the heating element and the reflector, arranged so as to essentially insulate, electrically, the reflector from the heating element.

5. A device according to claim 1, wherein

the controller is configured to apply a current and/or a voltage to the heating element, the latter being a resistive heating element, to energize the heating element, so as to heat the PCM and thereby reversibly change a refractive index and/or an absorption of said PCM.

6. A device according to claim 5, wherein:

the device further comprises an electrically conducting layer, in which the heating element is intercalated, at the level of said layer structure, whereby two portions of the electrically conducting layer are on respective lateral sides of the heating element, in contact therewith; and

the controller comprises two terminals contacting a respective one of said two portions, to apply said current and/or voltage to the heating element.

7. A device according to claim 1, wherein

the controller is configured to energize the heating element, according to at least two distinct signals, so as for the heating element to apply at least two distinct heat pulses, respectively, and reversibly switch the PCM to said at least two switchable states, respectively.

8. A device according to claim 1, wherein

the PCM comprises one or more of the following compounds:

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

9. A device according to claim 1, wherein

the PCM comprises one of:

Ge₂Sb₂Te₅;

GeTe; and

Ag₃In₄Sb₇₆Te₁₇.

10. A device according to claim 1, wherein

the PCM has an average thickness that is between 3 nm and 15 nm.

11. A device according to claim 1, wherein

the heating element comprises one or more of the following:

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

12. A device according to claim 1, comprising:

a set of thermally conducting, optical reflectors;

a set of thermally conducting spacers, each above a respective one of the reflectors, wherein the spacers have substantially different thicknesses and are, each, transmissive to light;

a set of phase change materials, or PCMs, each above a respective one of the spacers, so as to form, together with said set of spacers and said set of reflectors, a set of layer structures, wherein each of the PCMs has at least two, reversibly switchable states, in which it exhibits two different values of refractive index;

a set of heating elements, each being;

arranged opposite to a respective one of the PCMs with respect to a respective one of reflectors;

in thermal communication with said respective one of the PCMs via a respective one of the reflectors and a respective one of the spacers; and

electrically insulated from said respective one of the PCMs,

wherein,

the controller is configured to independently energize the heating elements, so as to independently heat the PCMs and thereby reversibly change a refractive index and/or an absorption thereof, whereby the refractive index and/or the absorption of each of the PCMs is independently controllable via the controller.

13. A device according to claim 12, further comprising

a set of pixels, each of said pixel comprising a set of layer structures such as said set of layer structures.

14. A display device, comprising a device according to claim 1, so as to form a set of pixels, each having a layer structure that includes:

said PCM; and

said heating element, the latter electrically insulated from the PCM and in thermal communication with the PCM in the layer structure, and wherein the display device further comprises;

said controller, the latter configured to energize any of the pixels, so as to independently heat a PCM of said any of the pixels and thereby reversibly change a refractive index and/or an absorption thereof; and

an arrangement of pairs of electrodes, each of the pairs of electrodes in electrical communication with a heating element of one of the pixels, so as for each of the pixels to be individually addressable by the controller in the display device.

15. The display device according to claim 14, wherein

each of the pairs of electrodes are in electrical communication with the heating element of one of the pixels through a via extending parallel to a stacking direction of the layer structure of said one of the pixel.

16. The display device according to claim 15, wherein

said via is in electrical contact with a drain terminal of a thin-film transistor, or TFT, whose gate terminal and source terminal are in electrical contact with a respective electrode of said each of the pairs of electrodes, so as for a voltage applied at the gate terminal to control a current between the source terminal and the drain terminal of the TFT, in operation.

17. The display device according to claim 15, wherein

said heating element is further in electrical communication with a thermally conducting, optical reflector, through another via, which extends parallel to a stacking direction of the layer structure of said one of the pixel, the reflector being further electrically conducting, whereby a current passing through the heating element can be drained through said optical reflector, in operation.

18. The display device according to claim 15, wherein

said heating element is further in electrical communication with a common electrode of the display device, through another via, the latter extending parallel to a stacking direction of the layer structure of said one of the pixel, each of the vias extending between an average plane of said arrangement of pairs of electrodes and an average plane of the heating element of said one of the pixels, whereby a current passing through the heating element can be drained through the common electrode, in operation.

19. A method for controlling an optical device as in claim 1, the method comprising

repeatedly energizing, via the controller, a heating element of said optical device, so as to heat a PCM of the optical device, to reversibly change a refractive index and/or an absorption of said PCM.

20. The method according to claim 19, wherein repeatedly energizing comprises:

energizing, during a time duration t₁, a heating element, to heat said PCM according to a first temporal heat profile and thereby switch said PCM from a first state to a second state; and

subsequently energizing, during a time duration t₂, the heating element, to heat said PCM according to a second temporal heat profile and thereby switch said PCM back to the first state,

wherein,

said first temporal heat profile exhibits a maximal temperature T₁ and said second temporal heat profile exhibits a maximal temperature T₂, with t₁>

t₂ and T₂>

T_m>

T₁>

T_c, wherein T_m and T_c respectively correspond to a melting temperature and a crystallization temperature of said PCM.