US20120287707A1 - Optoelectronic memory devices - Google Patents
Optoelectronic memory devices Download PDFInfo
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- US20120287707A1 US20120287707A1 US13/558,541 US201213558541A US2012287707A1 US 20120287707 A1 US20120287707 A1 US 20120287707A1 US 201213558541 A US201213558541 A US 201213558541A US 2012287707 A1 US2012287707 A1 US 2012287707A1
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- G—PHYSICS
- G11—INFORMATION STORAGE
- G11C—STATIC STORES
- G11C13/00—Digital stores characterised by the use of storage elements not covered by groups G11C11/00, G11C23/00, or G11C25/00
- G11C13/0002—Digital stores characterised by the use of storage elements not covered by groups G11C11/00, G11C23/00, or G11C25/00 using resistive RAM [RRAM] elements
- G11C13/0004—Digital stores characterised by the use of storage elements not covered by groups G11C11/00, G11C23/00, or G11C25/00 using resistive RAM [RRAM] elements comprising amorphous/crystalline phase transition cells
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- G—PHYSICS
- G11—INFORMATION STORAGE
- G11C—STATIC STORES
- G11C13/00—Digital stores characterised by the use of storage elements not covered by groups G11C11/00, G11C23/00, or G11C25/00
- G11C13/0002—Digital stores characterised by the use of storage elements not covered by groups G11C11/00, G11C23/00, or G11C25/00 using resistive RAM [RRAM] elements
- G11C13/0009—RRAM elements whose operation depends upon chemical change
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- G—PHYSICS
- G11—INFORMATION STORAGE
- G11C—STATIC STORES
- G11C13/00—Digital stores characterised by the use of storage elements not covered by groups G11C11/00, G11C23/00, or G11C25/00
- G11C13/0002—Digital stores characterised by the use of storage elements not covered by groups G11C11/00, G11C23/00, or G11C25/00 using resistive RAM [RRAM] elements
- G11C13/0021—Auxiliary circuits
- G11C13/004—Reading or sensing circuits or methods
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- G—PHYSICS
- G11—INFORMATION STORAGE
- G11C—STATIC STORES
- G11C13/00—Digital stores characterised by the use of storage elements not covered by groups G11C11/00, G11C23/00, or G11C25/00
- G11C13/04—Digital stores characterised by the use of storage elements not covered by groups G11C11/00, G11C23/00, or G11C25/00 using optical elements ; using other beam accessed elements, e.g. electron or ion beam
- G11C13/047—Digital stores characterised by the use of storage elements not covered by groups G11C11/00, G11C23/00, or G11C25/00 using optical elements ; using other beam accessed elements, e.g. electron or ion beam using electro-optical elements
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- H—ELECTRICITY
- H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10N70/00—Solid-state devices without a potential-jump barrier or surface barrier, and specially adapted for rectifying, amplifying, oscillating or switching
- H10N70/20—Multistable switching devices, e.g. memristors
- H10N70/257—Multistable switching devices, e.g. memristors based on radiation or particle beam assisted switching, e.g. optically controlled devices
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- H—ELECTRICITY
- H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10N70/00—Solid-state devices without a potential-jump barrier or surface barrier, and specially adapted for rectifying, amplifying, oscillating or switching
- H10N70/801—Constructional details of multistable switching devices
- H10N70/881—Switching materials
- H10N70/883—Oxides or nitrides
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- G—PHYSICS
- G11—INFORMATION STORAGE
- G11C—STATIC STORES
- G11C13/00—Digital stores characterised by the use of storage elements not covered by groups G11C11/00, G11C23/00, or G11C25/00
- G11C13/04—Digital stores characterised by the use of storage elements not covered by groups G11C11/00, G11C23/00, or G11C25/00 using optical elements ; using other beam accessed elements, e.g. electron or ion beam
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- G—PHYSICS
- G11—INFORMATION STORAGE
- G11C—STATIC STORES
- G11C13/00—Digital stores characterised by the use of storage elements not covered by groups G11C11/00, G11C23/00, or G11C25/00
- G11C13/0002—Digital stores characterised by the use of storage elements not covered by groups G11C11/00, G11C23/00, or G11C25/00 using resistive RAM [RRAM] elements
- G11C13/0021—Auxiliary circuits
- G11C13/004—Reading or sensing circuits or methods
- G11C2013/0054—Read is performed on a reference element, e.g. cell, and the reference sensed value is used to compare the sensed value of the selected cell
Definitions
- the present invention relates to memory devices, and more specifically, to optoelectronic memory devices.
- a memory cell in a typical semiconductor memory device usually comprises one or more transistors and can store one of two possible values depending on the voltage potential of a certain node of the memory cell. For instance, the memory cell can be considered storing a 1 if the node is at 5V and storing a 0 if the node is at 0V. As a result, the memory cell is an electronic memory cell.
- an appropriate voltage potential is applied to the node (or another node) of the electronic memory cell.
- the voltage potential of the node (or another node) of the electronic memory cell can be sensed and then amplified by a sensor-amplifier (sense-amp) circuit.
- an optoelectronic memory device that (a) can be written optically (i.e., by light) or electrically (by applying voltage) and/or (b) can be read optically (i.e., by light) or electrically (by sensing voltage).
- the present invention provides a method, comprising providing a resistive/reflective region on a substrate, wherein the resistive/reflective region comprises a material having a characteristic of changing the material's reflectance due to a phase change in the material; sending an electric current through the resistive/reflective region so as to cause a reflectance change in the resistive/reflective region from a first reflectance value to a second reflectance value different from the first reflectance value; and optically reading the reflectance change in the resistive/reflective region.
- the present invention also provides a method, comprising providing a resistive/reflective region on a substrate, wherein the resistive/reflective region comprises a material having a characteristic of changing the material's resistance due to the material absorbing heat; projecting a laser beam on the resistive/reflective region so as to cause a resistance change in the resistive/reflective region from a first resistance value to a second resistance value different from the first resistance value; and electrically reading the resistance change in the resistive/reflective region.
- the present invention also provides a structure, comprising (a) N regular resistive/reflective regions on a substrate, N being a positive integer, wherein the N regular resistive/reflective regions comprise a material having a characteristic of changing the material's resistance and reflectance due to the material absorbing heat; (b) N sense-amp circuits electrically coupled one-to-one to the N regular resistive/reflective regions, wherein each sense-amp circuit of the N sense-amp circuits is adapted for recognizing a resistance change in the associated regular resistive/reflective region; and (c) a light source/light detecting device optically coupled to the N regular resistive/reflective regions, wherein the light source/light detecting device is adapted for recognizing a reflectance change in each regular resistive/reflective region of the N regular resistive/reflective regions.
- the present invention provides an optoelectronic memory device that (a) can be written optically (i.e., by light) or electrically (by applying voltage) and/or (b) can be read optically (i.e., by light) or electrically (by sensing voltage).
- FIG. 1 illustrates an optoelectronic memory device, in accordance with embodiments of the present invention.
- FIG. 2 illustrates one embodiment of optoelectronic memory cells of the optoelectronic memory device of FIG. 1 , in accordance with embodiments of the present invention.
- FIG. 3 illustrates how an applied voltage pulse affects the resistance of the optoelectronic memory cell of FIG. 2 , in accordance with embodiments of the present invention.
- FIG. 4 illustrates how an applied voltage affects the resistance of the optoelectronic memory cell of FIG. 2 , in accordance with embodiments of the present invention.
- FIG. 1 illustrates an optoelectronic memory device 100 , in accordance with embodiments of the present invention. More specifically, the optoelectronic memory device 100 comprises, illustratively, two optoelectronic memory cells (OEMC) 110 a and 110 r . The optoelectronic memory device 100 further comprises a switch 120 for applying voltage potentials Vcc and V WR to the OEMC 110 a and 110 r in a manner controlled by the control signals Va and Vr (further details are discussed below).
- OEMC optoelectronic memory cells
- the optoelectronic memory device 100 further comprises a switch 130 , a sensor-amplifier (sense-amp) circuit 140 , and a light source/light detecting device 150 .
- the switch 130 electrically couples the OEMC 110 a and 110 r to the sense-amp circuit 140 in a manner controlled by the control signal Vr, whereas the light source/light detecting device 150 is optically coupled to the OEMC 110 a and 110 r (further details are discussed below).
- FIG. 2 illustrates one embodiment of the OEMC 100 a of FIG. 1 , in accordance with embodiments of the present invention. More specifically, the OEMC 100 a comprises a resistive/reflective region 210 (comprising tantalum nitride TaN in one embodiment) embedded in a dielectric layer 240 .
- the dielectric layer 240 (comprising silicon dioxide SiO 2 in one embodiment) is formed on a semiconductor (e.g., silicon) layer 250 .
- the TaN resistive/reflective region 210 is electrically coupled to two electrically conducting lines 220 a and 220 b through two vias 230 a and 230 b , respectively.
- the electrically conducting lines 220 a and 220 b comprise aluminum (Al) or Copper (Cu) or any other metals
- the vias 230 a and 230 b comprise tungsten (W) or Cu or any other metals.
- the Al line 230 a of the OEMC 100 a is coupled to the switch 120 ( FIG. 1 ) whereas the Al line 230 b of the OEMC 100 a is coupled to ground ( FIG. 1 ).
- the fabrication of the OEMC 100 a can start out with the silicon layer 250 .
- a SiO 2 layer 240 a (the lower portion of the silicon dioxide layer 240 ) is formed on top of the silicon layer 250 by, illustratively, CVD (chemical vapor deposition) of SiO 2 .
- the TaN resistive/reflective region 210 is formed on top of the SiO 2 layer 240 a .
- the TaN resistive/reflective region 210 is formed on top of the SiO 2 layer 240 a by (i) blanket depositing a TaN layer (not shown) on top of the SiO 2 layer 240 a and then (ii) directionally and selectively etching the deposited TaN layer such that what remains of the deposited TaN layer is the TaN resistive/reflective region 210 .
- a SiO 2 layer 240 b (the upper portion of the silicon dioxide layer 240 ) is formed on top of the SiO 2 layer 240 a and the TaN resistive/reflective region 210 by illustratively CVD of SiO 2 .
- the TaN resistive/reflective region 210 is embedded in the SiO 2 layer 240 .
- the two W vias 230 a and 230 b are formed (i) in the SiO 2 layer 240 b and (ii) in electrical contact with the TaN resistive/reflective region 210 .
- the two W vias 230 a and 230 b are formed by (a) creating two holes 230 a and 230 b by any conventional lithographic process such that the TaN resistive/reflective region 210 is exposed to the surrounding ambient via the holes 230 a and 230 b , then (b) blanket depositing a tungsten layer (not shown) so as to fill the two holes 230 a and 230 b with tungsten, and then (c) planarizing the deposited tungsten layer until a top surface 242 of the SiO 2 layer 240 b is exposed to the surrounding ambient.
- the two Al lines 220 a and 220 b are formed (i) on top of SiO 2 layer 240 b and (ii) in electrical contact with the two W vias 230 a and 230 b , respectively.
- the two Al lines 220 a and 220 b are formed by (a) blanket depositing an Al layer (not shown) on top of the SiO 2 layer 240 b and the two W vias 230 a and 230 b , and then (b) directionally and selectively etching the deposited Al layer such that what remain of the deposited Al layer are the two Al lines 220 a and 220 b.
- the structure of the OEMC 110 r is similar to the structure of the OEMC 110 a described above. Moreover, the OEMC 110 r is coupled to the switch 120 and ground ( FIG. 1 ) in a manner similar to the manner in which the OEMC 110 a is coupled to the switch 120 and ground ( FIG. 1 ).
- FIG. 3 shows a plot 300 illustrating how an applied voltage pulse affects the resistance of the TaN resistive/reflective region 210 of the optoelectronic memory cell 110 a of FIG. 2 , in accordance with embodiments of the present invention. More specifically, the inventors of the present invention have found that a voltage pulse applied across the TaN resistive/reflective region 210 ( FIG. 2 ) changes both the resistance and the reflectance of the TaN resistive/reflective region 210 ( FIG. 2 ). The reflectance is defined as the ratio of the photon flux reflected by a surface to the photon flux incident on the surface.
- the applied voltage pulse can have a triangular shape. More specifically, the applied voltage pulse comprises an increase from 0V to a peak voltage and then a voltage drop back to 0V.
- the inventors of the present invention have found that, for a particular size of the TaN resistive/reflective region 210 ( FIG. 2 ), if the peak voltage of the applied voltage pulse is between V 1 and V 2 (for example, V 1 and V 2 can be 3V and 4V, respectively, represented by segment B-C of the plot 300 is applicable), then both the resistance and the reflectance of the TaN resistive/reflective region 210 ( FIG. 2 ) change as a result of the applied voltage pulse. More specifically, in this segment B-C of the plot 300 , the higher the peak voltage of the applied voltage pulse, the higher the resulting resistance and the reflectance of the TaN resistive/reflective region 210 ( FIG. 2 ).
- the resistance of the TaN resistive/reflective region 210 ( FIG. 2 ) is originally R 0 , and that a voltage pulse having a peak voltage of V 2 (i.e., 4V in the example above) is applied across the TaN resistive/reflective region 210 ( FIG. 2 ). After the pulse is removed, the resistance of the TaN resistive/reflective region 210 ( FIG. 2 ) is R 1 . Also after the pulse is removed, the TaN resistive/reflective region 210 ( FIG. 2 ) has a higher reflectance.
- V 2 peak voltage of V 2
- the change in resistance and reflectance of the TaN resistive/reflective region 210 ( FIG. 2 ) in the example above with respect to segment B-C of the plot 300 is irreversible.
- V 1 peak voltage
- the resistance and reflectance of the TaN resistive/reflective region 210 ( FIG. 2 ) would not change back to original values, but remain essentially unchanged (i.e., R 1 for resistance).
- the operation of the optoelectronic memory device 100 is as follows, assuming that the OEMC 110 a and 110 r operate in the segment B-C of the plot 300 ( FIG. 3 ).
- the OEMC 110 a can be electrically written. Assuming that a 1 is to be written into the OEMC 110 a , then Va and Vr can be adjusted such that the switch 120 electrically couples OEMC 110 a to signal V WR such that a voltage pulse of signal V wR having a peak voltage of V 2 (i.e., 4V in the example above) is applied across the OEMC 110 a . As a result of the pulse, the resistance of the TaN resistive/reflective region 210 ( FIG. 2 ) change from R 0 (initial resistance) to and stays at R 1 . Also as a result of the pulse, the reflectance of the TaN resistive/reflective region 210 ( FIG. 2 ) increases (and remains high even after the pulse is removed).
- the content of the OEMC 110 a can be electrically read. More specifically, Va and Vr can be adjusted such that the switch 120 electrically couples the OEMCs 110 a and 110 r to Vcc and such that the switch 130 electrically couples the OEMCs 110 a and 110 r to the sense-amp circuit 140 . Because the resistance of the OEMC 110 a is high (R 1 ) while the resistance of the OEMC 110 r stays at R 0 , the sense-amp circuit 140 can recognize such a difference (by comparing the voltage drops across the OEMC 110 a and 110 r ) and accordingly generates a 1 at its output Vout, indicating that the OEMC 110 a stores a 1. It should be noted here that the OEMC 110 r is used as a reference memory cell for reading the content of the OEMC 110 a.
- the content of the OEMC 110 a can be optically read.
- the light source/light detecting device 150 can generate identical incident beams 162 a and 162 r (e.g., lasers) to the OEMCs 110 a and 110 r , respectively, and receives the reflected beams 164 a and 164 r from the OEMCs 110 a and 110 r , respectively.
- the incident laser beams 162 a and 162 r have 1.3 ⁇ m wavelength with a laser pulse duration of 15 ns and with a laser energy in a range of 0.035 ⁇ j to 0.095 ⁇ j.
- the light source/light detecting device 150 can recognize the difference in the intensities of the reflected beams 164 a and 164 r from the OEMCs 110 a and 110 r , respectively, and accordingly generates a 1 indicating that OEMC 110 a stores a 1. It should be noted here that the OEMC 110 r is used as a reference memory cell for reading the content of the OEMC 110 a.
- an incident beam e.g., a laser
- an incident beam can have the same effect as a voltage pulse with respect to changing the resistance and reflectance of the TaN resistive/reflective region 210 ( FIG. 2 ).
- both the laser beam and the voltage pulse have the same effect of generating heat in the TaN resistive/reflective region 210 ( FIG. 2 ), resulting in a phase change in the material of resistive/reflective region 210 ( FIG. 2 ) leading to the change in the resistance and reflectance of the TaN resistive/reflective region 210 ( FIG. 2 ) as described above.
- the voltage pulse In the case of the voltage pulse, the voltage pulse generates an electric current that passes through and hence generates heat in the TaN resistive/reflective region 210 ( FIG. 2 ). In case of the laser, the energy of the laser transforms into heat in the TaN resistive/reflective region 210 ( FIG. 2 ).
- the OEMC 110 a can be optically written. More specifically, assuming that a 1 is to be written into the OEMC 110 a , then the light source/light detecting device 150 can generate the incident beam 162 a (e.g., a laser) at sufficient intensity to the OEMC 110 a such that it is as if a voltage pulse with a peak voltage of V 2 (i.e., 4V in the example above) were applied across the OEMC 110 a .
- V 2 peak voltage of V 2
- the incident laser beams 162 a and 162 r have 1.3 ⁇ m wavelength with a laser pulse duration of 15 ns and with a laser energy in a range of 0.6 ⁇ j to 1.5 ⁇ j.
- both the resistance and reflectance of the TaN resistive/reflective region 210 increase. This increase in the resistance and reflectance of the TaN resistive/reflective region 210 ( FIG. 2 ) can be subsequently detected electrically and optically as described above.
- the OEMC 110 a operates in the segment X-Y of the plot 400 ( FIG. 4 ).
- the OEMC 110 a can simultaneously be written electrically and read optically, and as a result, can be used to convert an electrical signal into an optical signal.
- the TaN resistive/reflective region 210 ( FIG. 2 ) of the OEMC 110 a when the applied voltage is 0V (a 0 for the electrical signal), the TaN resistive/reflective region 210 ( FIG. 2 ) of the OEMC 110 a has a first reflectance.
- the light source/light detecting device 150 can detect the same reflectance for both OEMCs 110 a and 110 r and accordingly generates a 0 for the optical signal.
- the TaN resistive/reflective region 210 ( FIG. 2 ) of the OEMC 110 a has a second reflectance higher than the first reflectance.
- the light source/light detecting device 150 can detect the reflectance difference between the reflectances of the OEMCs 110 a and 110 r and accordingly generates a 1 for the optical signal.
- the OEMC 110 a can be used to convert an electrical signal into an optical signal.
- laser wavelengths of 532 nm, 1064 nm, or 1340 nm can be used for the incident laser beams 162 a and 162 r used to read the content of the OEMC 110 a while the OEMC 110 a operates in the segment X-Y of the plot 400 ( FIG. 4 ).
- the OEMC 110 a can simultaneously be written optically and read electrically, and as a result, can be used to convert an optical signal into an electrical signal.
- the energy of the lasers used for optically writing the OEMC 110 a when the OEMC 110 a operates in the segment X-Y of the plot 400 ( FIG. 4 ) can be higher than the energy of the lasers used for optically reading the OEMC 110 a when the OEMC 110 a operates in the segment B-C of the plot 300 ( FIG. 3 ) but lower than the energy of the lasers used for optically writing the OEMC 110 a when the OEMC 110 a operates in the segment B-C of the plot 300 ( FIG. 3 ).
- the TaN resistive/reflective region 210 ( FIG. 2 ) of the OEMC 110 a when the intensity of incident laser beam 162 a is zero (a 0 for the optical signal), the TaN resistive/reflective region 210 ( FIG. 2 ) of the OEMC 110 a has a first resistance.
- the sense-amp circuit 140 can detect the same resistance for both OEMCs 110 a and 110 r and accordingly generates a 0 for the electrical signal.
- the TaN resistive/reflective region 210 ( FIG. 2 ) of the OEMC 110 a has a second resistance higher than the first resistance.
- the sense-amp circuit 140 can detect the resistance difference between the resistances of the OEMCs 110 a and 110 r and accordingly generates a 1 for the electrical signal.
- the OEMC 110 a can be used to convert an optical signal into an electrical signal.
- the sense-amp circuit 140 and the light source/light detecting device 150 need to be more sensitive so as to detect small changes of the resistance and the reflectance of the TaN resistive/reflective region 210 ( FIG. 2 ).
- the OEMC 110 a can function as a one-time write optoelectronic memory cell which, after be written, can be read many times either electrically or optically.
- the OEMC 110 a can function as an electrical-optical converter for converting back and forth between electrical digital signals and optical digital signals.
- the optoelectronic memory device 100 can comprise N OEMCs (not shown) essentially identical to the OEMC 110 a each of which can store one bit of information (N is a positive integer).
- N is a positive integer.
- a write switch not shown but similar to the switch 120
- a read switch not shown but similar to the switch 130
- a sense-amp circuit not shown but similar to the sense-amp circuit 140
- each of these N OEMCs is optically coupled to the light source/light detecting device 150 in a manner similar to that of the OEMC 110 a .
- each of these N OEMCs is similar to that of the OEMC 110 a .
- all the N OEMCs of the optoelectronic memory device 100 share the same reference OEMC 110 r .
- each of the N OEMCs of the optoelectronic memory device 100 can have its own reference OEMC.
- the resistive/reflective region 210 comprises tantalum nitride TaN.
- the resistive/reflective region 210 can be a TaN composite stack including multiple layers (not shown).
- the resistive/reflective region 210 can be a SiN/TaN/SiO2/SiN composite stack, a SiN/TaN/SiN composite stack, SiN/SiO2/TaN/SiN composite stack, or any other composite stack that includes a TaN core layer.
- the dielectric layer 240 comprises silicon dioxide SiO 2 .
- the dielectric layer 240 can comprise a low-K material such as SiCOH, SiLK, and polymers, etc.
- the resistance of the resistive/reflective region 210 increases when it absorbs a small heat amount that comes from either a voltage source or a low-energy laser. This is the case shown in FIG. 4A when the material of the resistive/reflective region 210 ( FIG. 2 ) has a positive temperature coefficient of resistance (TCR).
- the resistance of the resistive/reflective region 210 ( FIG. 2 ) can decrease when it absorbs a small heat amount that comes from either a voltage source or a low-energy laser. This is the case shown in FIG. 4B when the material of the resistive/reflective region 210 ( FIG. 2 ) has a negative TCR.
- TaN can have either positive or negative TCR depending on the TaN film fabrication process. However, whether the material of the resistive/reflective region 210 ( FIG. 2 ) has a positive or negative TCR, the light source/light detecting device 150 can recognize a difference (if any) in the reflected beams from the OEMCs 110 a and 110 r and operate accordingly.
- the reflectance of the resistive/reflective region 210 increases when the resistive/reflective region 210 ( FIG. 2 ) absorbs a small heat amount that comes from either a voltage source or a low-energy laser.
- the reflectance of the resistive/reflective region 210 can decrease when the resistive/reflective region 210 ( FIG. 2 ) absorbs a small heat amount that comes from either a voltage source or a low-energy laser.
- a resistance increase does not necessarily occurs hand-in-hand with a reflectance increase in either reversible or irreversible case.
- a resistance decrease does not necessarily occur hand-in-hand with a reflectance decrease in either reversible or irreversible case.
- the inventors of the present invention have found that for a particular resistive/reflective region 210 ( FIG. 2 ), at some heat absorption level, the resistance of the sample 210 increases above the original resistance value while the reflectivity goes below the original reflectance value. But at a certain higher heat absorption level, the resistance of the sample 210 goes below the original resistance value while the reflectivity goes above the original reflectance value.
Abstract
Description
- This application is a continuation application claiming priority to Ser. No. 12/842,158, filed Jul. 23, 2010 which is a divisional application claiming priority to Ser. No. 11/161,941, filed Aug. 23, 2005, now U.S. Pat. No. 7,768,815 issued Aug. 3, 2010.
- 1. Technical Field
- The present invention relates to memory devices, and more specifically, to optoelectronic memory devices.
- 2. Related Art
- A memory cell in a typical semiconductor memory device usually comprises one or more transistors and can store one of two possible values depending on the voltage potential of a certain node of the memory cell. For instance, the memory cell can be considered storing a 1 if the node is at 5V and storing a 0 if the node is at 0V. As a result, the memory cell is an electronic memory cell. In order to write the electronic memory cell, an appropriate voltage potential is applied to the node (or another node) of the electronic memory cell. In order to read the content of the electronic memory cell, the voltage potential of the node (or another node) of the electronic memory cell can be sensed and then amplified by a sensor-amplifier (sense-amp) circuit. However, electrical digital signal transmission is usually slower than optical digital signal propagation. Therefore, it would speed up the write and read cycles of the memory cell if either or both of the write and read cycles can be performed optically. As a result, there is a need for an optoelectronic memory device that (a) can be written optically (i.e., by light) or electrically (by applying voltage) and/or (b) can be read optically (i.e., by light) or electrically (by sensing voltage).
- The present invention provides a method, comprising providing a resistive/reflective region on a substrate, wherein the resistive/reflective region comprises a material having a characteristic of changing the material's reflectance due to a phase change in the material; sending an electric current through the resistive/reflective region so as to cause a reflectance change in the resistive/reflective region from a first reflectance value to a second reflectance value different from the first reflectance value; and optically reading the reflectance change in the resistive/reflective region.
- The present invention also provides a method, comprising providing a resistive/reflective region on a substrate, wherein the resistive/reflective region comprises a material having a characteristic of changing the material's resistance due to the material absorbing heat; projecting a laser beam on the resistive/reflective region so as to cause a resistance change in the resistive/reflective region from a first resistance value to a second resistance value different from the first resistance value; and electrically reading the resistance change in the resistive/reflective region.
- The present invention also provides a structure, comprising (a) N regular resistive/reflective regions on a substrate, N being a positive integer, wherein the N regular resistive/reflective regions comprise a material having a characteristic of changing the material's resistance and reflectance due to the material absorbing heat; (b) N sense-amp circuits electrically coupled one-to-one to the N regular resistive/reflective regions, wherein each sense-amp circuit of the N sense-amp circuits is adapted for recognizing a resistance change in the associated regular resistive/reflective region; and (c) a light source/light detecting device optically coupled to the N regular resistive/reflective regions, wherein the light source/light detecting device is adapted for recognizing a reflectance change in each regular resistive/reflective region of the N regular resistive/reflective regions.
- The present invention provides an optoelectronic memory device that (a) can be written optically (i.e., by light) or electrically (by applying voltage) and/or (b) can be read optically (i.e., by light) or electrically (by sensing voltage).
-
FIG. 1 illustrates an optoelectronic memory device, in accordance with embodiments of the present invention. -
FIG. 2 illustrates one embodiment of optoelectronic memory cells of the optoelectronic memory device ofFIG. 1 , in accordance with embodiments of the present invention. -
FIG. 3 illustrates how an applied voltage pulse affects the resistance of the optoelectronic memory cell ofFIG. 2 , in accordance with embodiments of the present invention. -
FIG. 4 illustrates how an applied voltage affects the resistance of the optoelectronic memory cell ofFIG. 2 , in accordance with embodiments of the present invention. -
FIG. 1 illustrates anoptoelectronic memory device 100, in accordance with embodiments of the present invention. More specifically, theoptoelectronic memory device 100 comprises, illustratively, two optoelectronic memory cells (OEMC) 110 a and 110 r. Theoptoelectronic memory device 100 further comprises aswitch 120 for applying voltage potentials Vcc and VWR to theOEMC - The
optoelectronic memory device 100 further comprises aswitch 130, a sensor-amplifier (sense-amp)circuit 140, and a light source/light detecting device 150. Theswitch 130 electrically couples theOEMC amp circuit 140 in a manner controlled by the control signal Vr, whereas the light source/light detecting device 150 is optically coupled to theOEMC -
FIG. 2 illustrates one embodiment of the OEMC 100 a ofFIG. 1 , in accordance with embodiments of the present invention. More specifically, the OEMC 100 a comprises a resistive/reflective region 210 (comprising tantalum nitride TaN in one embodiment) embedded in adielectric layer 240. The dielectric layer 240 (comprising silicon dioxide SiO2 in one embodiment) is formed on a semiconductor (e.g., silicon)layer 250. - In one embodiment, the TaN resistive/
reflective region 210 is electrically coupled to two electrically conductinglines vias lines vias Al line 230 a of the OEMC 100 a is coupled to the switch 120 (FIG. 1 ) whereas theAl line 230 b of the OEMC 100 a is coupled to ground (FIG. 1 ). - In one embodiment, the fabrication of the OEMC 100 a can start out with the
silicon layer 250. Next, in one embodiment, a SiO2 layer 240 a (the lower portion of the silicon dioxide layer 240) is formed on top of thesilicon layer 250 by, illustratively, CVD (chemical vapor deposition) of SiO2. - Next, in one embodiment, the TaN resistive/
reflective region 210 is formed on top of the SiO2 layer 240 a. Illustratively, the TaN resistive/reflective region 210 is formed on top of the SiO2 layer 240 a by (i) blanket depositing a TaN layer (not shown) on top of the SiO2 layer 240 a and then (ii) directionally and selectively etching the deposited TaN layer such that what remains of the deposited TaN layer is the TaN resistive/reflective region 210. - Next, in one embodiment, a SiO2 layer 240 b (the upper portion of the silicon dioxide layer 240) is formed on top of the SiO2 layer 240 a and the TaN resistive/
reflective region 210 by illustratively CVD of SiO2. As a result, the TaN resistive/reflective region 210 is embedded in the SiO2 layer 240. - Next, in one embodiment, the two
W vias reflective region 210. Illustratively, the twoW vias holes reflective region 210 is exposed to the surrounding ambient via theholes holes top surface 242 of the SiO2 layer 240 b is exposed to the surrounding ambient. - Next, in one embodiment, the two
Al lines W vias Al lines W vias Al lines - In one embodiment, the structure of the OEMC 110 r is similar to the structure of the
OEMC 110 a described above. Moreover, the OEMC 110 r is coupled to theswitch 120 and ground (FIG. 1 ) in a manner similar to the manner in which the OEMC 110 a is coupled to theswitch 120 and ground (FIG. 1 ). -
FIG. 3 shows aplot 300 illustrating how an applied voltage pulse affects the resistance of the TaN resistive/reflective region 210 of theoptoelectronic memory cell 110 a ofFIG. 2 , in accordance with embodiments of the present invention. More specifically, the inventors of the present invention have found that a voltage pulse applied across the TaN resistive/reflective region 210 (FIG. 2 ) changes both the resistance and the reflectance of the TaN resistive/reflective region 210 (FIG. 2 ). The reflectance is defined as the ratio of the photon flux reflected by a surface to the photon flux incident on the surface. In one embodiment, the applied voltage pulse can have a triangular shape. More specifically, the applied voltage pulse comprises an increase from 0V to a peak voltage and then a voltage drop back to 0V. - The inventors of the present invention have found that, for a particular size of the TaN resistive/reflective region 210 (
FIG. 2 ), if the peak voltage of the applied voltage pulse is between V1 and V2 (for example, V1 and V2 can be 3V and 4V, respectively, represented by segment B-C of theplot 300 is applicable), then both the resistance and the reflectance of the TaN resistive/reflective region 210 (FIG. 2 ) change as a result of the applied voltage pulse. More specifically, in this segment B-C of theplot 300, the higher the peak voltage of the applied voltage pulse, the higher the resulting resistance and the reflectance of the TaN resistive/reflective region 210 (FIG. 2 ). For example, assume the resistance of the TaN resistive/reflective region 210 (FIG. 2 ) is originally R0, and that a voltage pulse having a peak voltage of V2 (i.e., 4V in the example above) is applied across the TaN resistive/reflective region 210 (FIG. 2 ). After the pulse is removed, the resistance of the TaN resistive/reflective region 210 (FIG. 2 ) is R1. Also after the pulse is removed, the TaN resistive/reflective region 210 (FIG. 2 ) has a higher reflectance. - It should be noted that the change in resistance and reflectance of the TaN resistive/reflective region 210 (
FIG. 2 ) in the example above with respect to segment B-C of theplot 300 is irreversible. For illustration, assume that after the pulse described above is removed, another voltage pulse having a peak voltage of V1 (i.e., 3V in the example above) is applied across the TaN resistive/reflective region 210 (FIG. 2 ). The resistance and reflectance of the TaN resistive/reflective region 210 (FIG. 2 ) would not change back to original values, but remain essentially unchanged (i.e., R1 for resistance). -
FIG. 4A shows aplot 400 illustrating how an applied voltage affects the resistance of the optoelectronic memory cell ofFIG. 2 , in accordance with embodiments of the present invention. More specifically, the inventors of the present invention have found that both the resistance and the reflectance of the TaN resistive/reflective region 210 (FIG. 2 ) change reversibly in response to the applied voltage between 0V and V1 (in one case, V1=3V). For instance, when the applied voltage changes from 0V to V1, the resistance of the TaN resistive/reflective region 210 (FIG. 2 ) increases from R0 to R3. Also, although not shown, the reflectance of the TaN resistive/reflective region 210 (FIG. 2 ) increases (i.e., less transparent). However, when the applied voltage changes from V1 back to 0V, the resistance and reflectance of the TaN resistive/reflective region 210 (FIG. 2 ) change back to the original values (i.e., reversible). - With reference to
FIGS. 1-4A , in one embodiment, the operation of theoptoelectronic memory device 100 is as follows, assuming that theOEMC FIG. 3 ). - In one embodiment, the
OEMC 110 a can be electrically written. Assuming that a 1 is to be written into theOEMC 110 a, then Va and Vr can be adjusted such that theswitch 120electrically couples OEMC 110 a to signal VWR such that a voltage pulse of signal VwR having a peak voltage of V2 (i.e., 4V in the example above) is applied across theOEMC 110 a. As a result of the pulse, the resistance of the TaN resistive/reflective region 210 (FIG. 2 ) change from R0 (initial resistance) to and stays at R1. Also as a result of the pulse, the reflectance of the TaN resistive/reflective region 210 (FIG. 2 ) increases (and remains high even after the pulse is removed). - In one embodiment, the content of the
OEMC 110 a can be electrically read. More specifically, Va and Vr can be adjusted such that theswitch 120 electrically couples theOEMCs switch 130 electrically couples theOEMCs amp circuit 140. Because the resistance of theOEMC 110 a is high (R1) while the resistance of theOEMC 110 r stays at R0, the sense-amp circuit 140 can recognize such a difference (by comparing the voltage drops across theOEMC OEMC 110 a stores a 1. It should be noted here that theOEMC 110 r is used as a reference memory cell for reading the content of theOEMC 110 a. - In an alternative embodiment, the content of the
OEMC 110 a can be optically read. More specifically, the light source/light detecting device 150 can generate identical incident beams 162 a and 162 r (e.g., lasers) to the OEMCs 110 a and 110 r, respectively, and receives the reflectedbeams incident laser beams OEMC 110 r (as a result of the applied voltage pulse during the write cycle described above), the light source/light detecting device 150 can recognize the difference in the intensities of the reflectedbeams OEMC 110 a stores a 1. It should be noted here that theOEMC 110 r is used as a reference memory cell for reading the content of theOEMC 110 a. - The inventors of the present invention have found that an incident beam (e.g., a laser) can have the same effect as a voltage pulse with respect to changing the resistance and reflectance of the TaN resistive/reflective region 210 (
FIG. 2 ). This is because both the laser beam and the voltage pulse have the same effect of generating heat in the TaN resistive/reflective region 210 (FIG. 2 ), resulting in a phase change in the material of resistive/reflective region 210 (FIG. 2 ) leading to the change in the resistance and reflectance of the TaN resistive/reflective region 210 (FIG. 2 ) as described above. In the case of the voltage pulse, the voltage pulse generates an electric current that passes through and hence generates heat in the TaN resistive/reflective region 210 (FIG. 2 ). In case of the laser, the energy of the laser transforms into heat in the TaN resistive/reflective region 210 (FIG. 2 ). - As a result, in an alternative embodiment, instead of being electrically written as described above, the
OEMC 110 a can be optically written. More specifically, assuming that a 1 is to be written into theOEMC 110 a, then the light source/light detecting device 150 can generate theincident beam 162 a (e.g., a laser) at sufficient intensity to theOEMC 110 a such that it is as if a voltage pulse with a peak voltage of V2 (i.e., 4V in the example above) were applied across theOEMC 110 a. In one embodiment, theincident laser beams FIG. 2 ) increase. This increase in the resistance and reflectance of the TaN resistive/reflective region 210 (FIG. 2 ) can be subsequently detected electrically and optically as described above. - In an alternative embodiment, instead of operating in the segment B-C of the
plot 300 as described above, theOEMC 110 a operates in the segment X-Y of the plot 400 (FIG. 4 ). Operating in the segment X-Y of the plot 400 (FIG. 4 ), theOEMC 110 a can simultaneously be written electrically and read optically, and as a result, can be used to convert an electrical signal into an optical signal. - More specifically, in one embodiment, when the applied voltage is 0V (a 0 for the electrical signal), the TaN resistive/reflective region 210 (
FIG. 2 ) of theOEMC 110 a has a first reflectance. The light source/light detecting device 150 can detect the same reflectance for bothOEMCs FIG. 2 ) of theOEMC 110 a has a second reflectance higher than the first reflectance. The light source/light detecting device 150 can detect the reflectance difference between the reflectances of the OEMCs 110 a and 110 r and accordingly generates a 1 for the optical signal. In other words, theOEMC 110 a can be used to convert an electrical signal into an optical signal. In one embodiment, laser wavelengths of 532 nm, 1064 nm, or 1340 nm can be used for theincident laser beams OEMC 110 a while theOEMC 110 a operates in the segment X-Y of the plot 400 (FIG. 4 ). - Similarly, operating in the segment X-Y of the plot 400 (
FIG. 4 ), theOEMC 110 a can simultaneously be written optically and read electrically, and as a result, can be used to convert an optical signal into an electrical signal. In one embodiment, regarding theincident laser beams OEMC 110 a when theOEMC 110 a operates in the segment X-Y of the plot 400 (FIG. 4 ) can be higher than the energy of the lasers used for optically reading theOEMC 110 a when theOEMC 110 a operates in the segment B-C of the plot 300 (FIG. 3 ) but lower than the energy of the lasers used for optically writing theOEMC 110 a when theOEMC 110 a operates in the segment B-C of the plot 300 (FIG. 3 ). - More specifically, in one embodiment, when the intensity of
incident laser beam 162 a is zero (a 0 for the optical signal), the TaN resistive/reflective region 210 (FIG. 2 ) of theOEMC 110 a has a first resistance. The sense-amp circuit 140 can detect the same resistance for bothOEMCs incident laser beam 162 a is at a higher level (a 1 for the optical signal), the TaN resistive/reflective region 210 (FIG. 2 ) of theOEMC 110 a has a second resistance higher than the first resistance. The sense-amp circuit 140 can detect the resistance difference between the resistances of the OEMCs 110 a and 110 r and accordingly generates a 1 for the electrical signal. In other words, theOEMC 110 a can be used to convert an optical signal into an electrical signal. - It should be noted that because the changes of the resistance and the reflectance of the TaN resistive/reflective region 210 (
FIG. 2 ) when theOEMC 110 a operates in the segment X-Y of theplot 400 is smaller than when theOEMC 110 a operates in the segment B-C of theplot 300, the sense-amp circuit 140 and the light source/light detecting device 150 need to be more sensitive so as to detect small changes of the resistance and the reflectance of the TaN resistive/reflective region 210 (FIG. 2 ). - In summary, operating in the segment B-C of the
plot 300, theOEMC 110 a can function as a one-time write optoelectronic memory cell which, after be written, can be read many times either electrically or optically. In contrast, operating in the segment X-Y of theplot 400, theOEMC 110 a can function as an electrical-optical converter for converting back and forth between electrical digital signals and optical digital signals. - In one embodiment, with reference to
FIG. 1 , theoptoelectronic memory device 100 can comprise N OEMCs (not shown) essentially identical to theOEMC 110 a each of which can store one bit of information (N is a positive integer). For each of these N OEMCs, there needs to be (i) a write switch (not shown but similar to theswitch 120, (ii) a read switch (not shown but similar to the switch 130), and (iii) a sense-amp circuit (not shown but similar to the sense-amp circuit 140). Moreover, each of these N OEMCs is optically coupled to the light source/light detecting device 150 in a manner similar to that of theOEMC 110 a. The operation of each of these N OEMCs is similar to that of theOEMC 110 a. In one embodiment, all the N OEMCs of theoptoelectronic memory device 100 share thesame reference OEMC 110 r. Alternatively, each of the N OEMCs of theoptoelectronic memory device 100 can have its own reference OEMC. - It should be noted that the description of the embodiments above is sufficient such that a person with ordinary skill in the art could practice the invention without undue experimentation.
- With reference back to
FIG. 2 , in the embodiments described above, the resistive/reflective region 210 comprises tantalum nitride TaN. In general, the resistive/reflective region 210 can be a TaN composite stack including multiple layers (not shown). In one embodiment, the resistive/reflective region 210 can be a SiN/TaN/SiO2/SiN composite stack, a SiN/TaN/SiN composite stack, SiN/SiO2/TaN/SiN composite stack, or any other composite stack that includes a TaN core layer. Also, in the embodiments described above, thedielectric layer 240 comprises silicon dioxide SiO2. Alternatively, thedielectric layer 240 can comprise a low-K material such as SiCOH, SiLK, and polymers, etc. - In the embodiments described above, the resistance of the resistive/reflective region 210 (
FIG. 2 ) increases when it absorbs a small heat amount that comes from either a voltage source or a low-energy laser. This is the case shown inFIG. 4A when the material of the resistive/reflective region 210 (FIG. 2 ) has a positive temperature coefficient of resistance (TCR). Alternatively, the resistance of the resistive/reflective region 210 (FIG. 2 ) can decrease when it absorbs a small heat amount that comes from either a voltage source or a low-energy laser. This is the case shown inFIG. 4B when the material of the resistive/reflective region 210 (FIG. 2 ) has a negative TCR. - It should be noted that TaN can have either positive or negative TCR depending on the TaN film fabrication process. However, whether the material of the resistive/reflective region 210 (
FIG. 2 ) has a positive or negative TCR, the light source/light detecting device 150 can recognize a difference (if any) in the reflected beams from the OEMCs 110 a and 110 r and operate accordingly. - It should also be noted that the voltage values in
FIGS. 3 and 4 are for illustration only. Therefore, the scope of the claims are not in any way restricted to these values. - Similarly, in the embodiments described above, the reflectance of the resistive/reflective region 210 (
FIG. 2 ) increases when the resistive/reflective region 210 (FIG. 2 ) absorbs a small heat amount that comes from either a voltage source or a low-energy laser. Alternatively, the reflectance of the resistive/reflective region 210 (FIG. 2 ) can decrease when the resistive/reflective region 210 (FIG. 2 ) absorbs a small heat amount that comes from either a voltage source or a low-energy laser. - It should also be noted that a resistance increase does not necessarily occurs hand-in-hand with a reflectance increase in either reversible or irreversible case. Similarly, a resistance decrease does not necessarily occur hand-in-hand with a reflectance decrease in either reversible or irreversible case. For instance, the inventors of the present invention have found that for a particular resistive/reflective region 210 (
FIG. 2 ), at some heat absorption level, the resistance of thesample 210 increases above the original resistance value while the reflectivity goes below the original reflectance value. But at a certain higher heat absorption level, the resistance of thesample 210 goes below the original resistance value while the reflectivity goes above the original reflectance value. - While particular embodiments of the present invention have been described herein for purposes of illustration, many modifications and changes will become apparent to those skilled in the art. Accordingly, the appended claims are intended to encompass all such modifications and changes as fall within the true spirit and scope of this invention.
Claims (20)
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US7768815B2 (en) | 2005-08-23 | 2010-08-03 | International Business Machines Corporation | Optoelectronic memory devices |
US8542518B2 (en) * | 2010-03-31 | 2013-09-24 | Hewlett-Packard Development Company, L.P. | Photo-responsive memory resistor and method of operation |
FR2981229B1 (en) * | 2011-10-10 | 2013-12-27 | Commissariat Energie Atomique | DEVICE FOR CONVERTING CURRENT PULSES TO VOLTAGE PULSES. |
CN103559909B (en) * | 2013-10-31 | 2016-06-01 | 中国科学院上海微系统与信息技术研究所 | The phase change memory structure that the mixing of a kind of photoelectricity stores and its preparation method |
CN103730573B (en) * | 2014-01-15 | 2017-11-10 | 中国科学院宁波材料技术与工程研究所 | A kind of Multifunctional photoelectric processor construction unit, its preparation method and application |
BR112017020042A2 (en) | 2015-04-23 | 2018-06-05 | Halliburton Energy Services Inc | spectrally programmable optical device and optical method |
WO2016171700A1 (en) | 2015-04-23 | 2016-10-27 | Halliburton Energy Services, Inc. | Spectrally programmable memristor-based optical computing |
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Also Published As
Publication number | Publication date |
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CN1921010A (en) | 2007-02-28 |
US20100290264A1 (en) | 2010-11-18 |
US8288747B2 (en) | 2012-10-16 |
US7768815B2 (en) | 2010-08-03 |
TW200709205A (en) | 2007-03-01 |
US20130258765A1 (en) | 2013-10-03 |
US8945955B2 (en) | 2015-02-03 |
US20070051875A1 (en) | 2007-03-08 |
CN1921010B (en) | 2010-05-26 |
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