Optically Gated Field-Emission Photocathodes Without Gate Capacitance
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Solution Overview
Problem
Current vacuum electronic devices are bulky and limited in miniaturization due to the use of thermionic emission cathodes, and alternative cold field emission technologies face limitations in frequency performance and voltage handling due to gate capacitance and parasitic current leakage.
Innovation Solution
The development of vacuum microelectronic devices with optically gated field emission photocathodes using wide or ultra-wide bandgap semiconductors, which are photoconductive and can be modulated by incident light, eliminating the need for an electronic gate and reducing parasitic current leakage, allowing for high-power and high-frequency applications in a compact form factor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If thermionic emission cathodes are used in vacuum electronic devices, then the devices can provide reliable electron emission, but the devices become bulky and cannot be miniaturized due to the high temperature (2000°C) required to boil off electrons
Solution Approach 1:
The patent changes the operating temperature parameter from 2000°C (thermionic) to room temperature (field emission), and switches the emission mechanism from thermal boiling to quantum tunneling. This parameter change enables miniaturization while maintaining reliable electron emission through the cold field emission photocathode approach.
Solution Approach 2:
The patent replaces the thermal emission mechanism (heat-driven electron boiling) with a quantum mechanical tunneling mechanism. By using photoconductive materials with wide bandgaps that enable field emission when illuminated, the system substitutes thermal physics with quantum effects, allowing compact device design.
2Temperature
If cold field emission cathodes with gate electrodes are used to modulate electron flow, then the devices can operate at room temperature, but the frequency performance is limited due to gate capacitance (Miller capacitance) and voltage handling is compromised due to parasitic current leakage at the gate
Solution Approach 1:
The patent extracts and removes the gate electrode from the conventional field emission structure. By using photoconductive modulation instead of electrical gating, the design eliminates the gate capacitance that limits frequency performance and the parasitic current leakage that compromises voltage handling. The electron flow is modulated optically rather than electrically.
Solution Approach 2:
The patent introduces light as an intermediary to modulate electron emission. Instead of using an electrical gate that directly contacts the cathode (causing capacitance and leakage issues), the system uses incident light on the photoconductive material to control electron tunneling. This optical intermediary eliminates the harmful electrical gate effects while maintaining modulation capability.
3Device complexity
If conventional field emission cathodes are used without photoconductive materials, then the structure is simple, but parasitic current leakage occurs when the device is in the off state due to thermal excitation of carriers
Solution Approach 1:
The patent employs composite material structures combining wide bandgap semiconductors (such as GaN, SiC, or diamond) with photoconductive properties. These materials provide both the field emission capability and the low leakage characteristics. The composite nature of these materials—combining wide bandgap for low thermal excitation with photoconductive properties for controllable emission—simultaneously reduces parasitic leakage and maintains structural feasibility.
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
These devices achieve fast pulse rates and reduced parasitic current leakage, enabling high-power and high-frequency performance while being miniaturized to the size of a microchip, bridging the gap between vacuum and solid-state electronics with increased performance and reduced volume and weight.
Implementation Method 1
An optically-gated field emission photocathode comprising, for example, wide bandgap (WBG) and ultra-wide bandgap (UWBG) semiconductors that are photoconductive
Implementation Method 2
cold field emission cathode that produces electric field enhancement at a sharp conductive tip (e.g., made from silicon or molybdenum). Electrons in these tips experience high enough electric fields to quantum mechanically tunnel into vacuum at room temperature.
Implementation Method 3
vacuum as the electronic medium
Data Source
AI summary
A vacuum electronic device is configured to provide electrical current that is configured to be optically modulated by incident light. The vacuum electronic device comprises an optically gated field emission photocathode comprising photoconductive material, an anode comprising a conductive material, and a gap between said photocathode and said anode. The gap comprises vacuum. The anode and photocathode are configured to receive a voltage across the anode and photocathode, such that when said photocathode is illuminated with said light, electrons are emitted from the photocathode and travel through the gap.