Optically Gated Transistor for Memristor Programming
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Solution Overview
Problem
Variable resistive memory devices, such as memristors, face challenges with sneak path currents that lead to false resistance readings and difficulties in programming due to the resistive nature of these devices, and existing selector devices like diodes and MOSFETs are not bidirectional or effective in controlling the programming conditions.
Innovation Solution
An optically gated transistor (OGT) device using alternating layers of germanium selenide (GeSe) with added elements like tin or copper, which conducts current bidirectionally in the presence of light and isolates memory devices from circuits in the absence of light, allowing for precise control of memristor programming through light intensity and voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a MOSFET transistor is used as a selector device for memristor programming, then the device can control current flow, but the drain-source on resistance creates a voltage divider that varies with memristor resistance, leading to unknown programming conditions and loss of control
Solution Approach 1:
The patent replaces the electric field-based control mechanism of conventional MOSFETs with an optical field-based control mechanism. The optically activated transistor uses light to control the formation of a conductive channel, eliminating the electrical voltage divider problem that occurs with MOSFETs when programming variable resistance memory devices. The optical control provides a different physical mechanism that doesn't suffer from the same electrical interference issues.
2Adaptability or versatility
If a diode is used as a selector device, then it can provide directional current control, but it does not operate bidirectionally and would require two opposite facing diodes for bipolar memristors, increasing chip area and fabrication complexity
Solution Approach 1:
The optically activated transistor serves multiple functions in a single device: it provides bidirectional current control, acts as a selector switch for memory programming, and enables precise control of programming conditions through optical activation. This multi-functional design eliminates the need for separate diodes for each direction, reducing chip area while maintaining versatility for bipolar memristor operation.
3Ease of operation
If fixed voltages are applied to bit and word lines with a MOSFET transistor, then the transistor can gate the memristor element, but the series combination of MOSFET on resistance and memristor resistance creates a voltage divider that varies with memristor state, preventing control of programmed resistance
Solution Approach 1:
The patent substitutes optical activation for electrical gating to control the transistor channel formation. By using light intensity and wavelength as control parameters instead of electrical voltages, the system achieves precise control of the conductive channel formation without the voltage divider problem that plagues electrical MOSFET gating. The optical control mechanism provides a more stable and controllable means of regulating current during memristor programming.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The OGT device effectively isolates memristors from sneak path currents, enabling accurate programming and multi-state operation by controlling the memristor state with light intensity, reducing unwanted current flows and providing a reliable selector function for variable resistive memory devices.
Implementation Method 1
The active material conducts current bidirectionally in a presence of light
Implementation Method 2
the active material conducts current bidirectionally in the presence of light and does not conduct appreciable current in the absence of light
Data Source
AI summary
An optically gated transistor (OGT) device that may be used as a selector device for one or more variable resistive memory devices. The OGT device isolates the one or more variable resistive memory devices when the OGT is not optically activated. The amount of current conducted by the OGT device is dependent on an intensity of light optically applied to the OGT device. The OGT device includes alternating layers of germanium selenide (GeSe) and GeSe plus an additional element deposited on a substrate. The OGT device includes only two electrodes connected to the alternating layers deposited on the substrate. The OGT device may generate an amplified electrical signal with respect to the magnitude of a received optical signal. The OGT device may be used to generate an optical signal having a different wavelength than the wavelength of a received optical signal.