Optical memory device and method therefor
View Patent ↗A nonvolatile memory device and method using phase changes in a substrate to alter optical properties of the substrate for the purpose of data storage. The memory device includes a substrate containing a phase change material having phases comprising amorphous and crystalline phases. The phase change material has optical properties that change depending on whether the phase change material is in the amorphous phase or the crystalline phase. The memory device is further equipped with one or more devices that generate light and transmit the light into the substrate, and one or more devices that cause the phase change material to change between the amorphous and crystalline phases thereof. At least one optical sensing device detects light that passes into the phase change material to the optical sensing device and generates electrical signals based thereon, which are converted into bit values if they exceed a threshold.
1. A memory device comprising:
a substrate containing a phase change material having phases comprising amorphous and crystalline phases, the phase change material having optical properties that change depending on whether the phase change material is in the amorphous phase or the crystalline phase;
means for generating light and transmitting the light into the substrate;
means for causing the phase change material to change between the amorphous and crystalline phases thereof by operating the light generating means to generate light pulses that pass into the substrate at an amplitude and pulse width sufficient to change the phase of the phase change material between the amorphous phase and the crystalline phase within regions of the substrate;
at least one optical sensing device adapted to detect light from the light generating means that passes into the phase change material to the optical sensing device and generate electrical signals based thereon; and
means for converting the electrical signals into bit values according to their level relative to a predetermined threshold.
2. The memory device of claim 1 , wherein the light generating means comprises an array of individual light sources.
3. The memory device of claim 2 , wherein the individual light sources are light emitting diodes.
4. The memory device of claim 2 , further comprising means for selectively activating the individual light sources within the array using row and column selection.
5. The memory device of claim 2 , wherein the optical sensing device comprises an array of individual optical sensing devices that are individually aligned with the individual light sources.
6. The memory device of claim 1 , wherein the optical sensing device comprises an array of CMOS light sensing devices, the memory device further comprising means for addressing the CMOS light sensing devices within the array by row and column.
7. The memory device of claim 6 , further comprising means for time multiplexing addresses of the CMOS light sensing devices.
8. The memory device of claim 7 , wherein the time multiplexing means simultaneously gives row and column addresses.
9. A memory device comprising:
a substrate containing a phase change material having phases comprising amorphous and crystalline phases, the phase change material having optical properties that change depending on whether the phase change material is in the amorphous phase or the crystalline phase;
means for generating light and transmitting the light into the substrate, wherein the light generating means comprises backlighting means;
means for causing the phase change material to change between the amorphous and crystalline phases thereof;
at least one optical sensing device adapted to detect light from the light generating means that passes into the phase change material to the optical sensing device and generate electrical signals based thereon, wherein the at least one optical sensing device is one of an array of individual optical sensing device; and
means for converting the electrical signals into bit values according to their level relative to a predetermined threshold;
wherein the means for causing the phase change material to change between the amorphous and crystalline phases thereof comprises an array of electrodes adapted to heat individual regions of the substrate associated with the individual optical sensing devices.
10. The memory device of claim 9 , wherein the array of individual optical sensing device is disposed between the backlighting means and the substrate.
11. The memory device of claim 9 , wherein the backlighting means comprises an array of individual light sources.
12. The memory device of claim 9 , wherein the backlighting means comprises a diffuse layer of light guide material.
13. A memory device comprising:
a substrate containing a phase change material having phases comprising amorphous and crystalline phases, the phase change material having optical properties that change depending on whether the phase change material is in the amorphous phase or the crystalline phase;
means for generating light and transmitting the light into the substrate;
means for causing the phase change material to change between the amorphous and crystalline phases thereof;
at least one optical sensing device adapted to detect light from the light generating means that passes into the phase change material to the optical sensing device and generate electrical signals based thereon, the optical sensing device comprising an array of CMOS light sensing devices, wherein the array of CMOS light sensing devices is one of a plurality of arrays of CMOS light sensing devices, each of the arrays being arranged as an internal bank of the memory device, the internal banks being spatially separated by logic structures;
means for addressing the CMOS light sensing devices within at least one of the arrays by row and column; and
means for converting the electrical signals into bit values according to their level relative to a predetermined threshold.
14. A method of storing data using a phase change material, the method comprising:
writing data by inducing a phase change in at least one region of a phase change material of a substrate, the phase change material having phases comprising amorphous and crystalline phases and having optical properties that change depending on whether the phase change material is in the amorphous phase or the crystalline phase, the writing step comprising activating at least one light source to generate a light pulse that passes into the substrate at an amplitude and pulse width sufficient to change the phase of the phase change material between the amorphous phase and the crystalline phase within a region of the substrate; and
reading data by activating at least one light source to generate light that passes into the substrate and is insufficient to change the phase of the phase change material within a region of the substrate, activating at least one optical sensing device of an array of optical sensing devices to detect light from the light source transmitted through the phase change material to the optical sensing device, generating at least one electrical signal with the at least one optical sensing device if light from the light source is detected, capturing the at least one electrical signal, determining whether the at least one electrical signal is above or below a threshold, and converting the at least one electrical signal into a bit value according to its level relative to a predetermined threshold.
15. The method of claim 14 , wherein the at least one light source is one of an array of light sources disposed at a first surface of the substrate.
16. The method of claim 15 , further comprising selectively activating the light sources within the array using row and column selection.
17. The method of claim 16 , wherein addressing of the light sources through rows and columns is time multiplexed.
18. The method of claim 16 , wherein addressing of the light sources by row and column is substantially simultaneous using a broad-side addressing scheme.
19. The method of claim 14 , wherein the writing step further comprises heating a region of the substrate to change the phase of the phase change material between the amorphous phase and the crystalline phase within the region.