Photosensitive FET With Patterned Gate Electrode for Rapid Charge Resetting
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Solution Overview
Problem
Existing field-effect transistors with two-dimensional channel materials and semiconducting photoactive layers face challenges in resetting charge states quickly, which limits their ability to perform correlated double-sampling effectively due to incomplete charge dissipation and long time-constants, making mechanical and liquid crystal shutters impractical for many applications.
Innovation Solution
A patterned second gate electrode is used to electrically reset field-effect phototransistors by controlling the charge neutrality in the photoactive material, allowing for rapid switching between light-sensitive and light-immune states, enabling efficient correlated double-sampling and high frame rates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If mechanical or liquid crystal shutters are used to reset photodetectors, then charge dissipation can be achieved, but the device becomes complex, noisy, and unreliable for many applications
Solution Approach 1:
The patent replaces mechanical shutters and liquid crystal shutters with an electrical resetting mechanism using a gate electrode. The gate electrode applies voltage to electrically dissipate charge from the photoactive layer, eliminating moving parts and complex shutter mechanisms while achieving reliable reset functionality.
Solution Approach 2:
The patent extracts the essential resetting function from complex mechanical shutter systems and implements it through a simple gate electrode voltage application. This separates the charge dissipation function from the mechanical actuation system, achieving reset reliability without the complexity of physical shutters.
2Speed
If mechanical shutters are used for resetting, then charge can be blocked, but the reset is incomplete and charge dissipation time-constant is too long
Solution Approach 1:
The patent replaces mechanical shutter-based charge blocking with electrical charge dissipation through the gate electrode. By applying appropriate voltage to the gate, charge is actively removed from the photoactive layer, achieving both fast reset speed and complete charge dissipation without the limitations of mechanical shutters.
3Quantity of substance
If photoactive layers are made thicker to increase light absorption, then spectral response expands, but charge transfer efficiency decreases
Solution Approach 1:
The patent makes the photoactive layer electrically dynamic by introducing a gate electrode that can actively control charge distribution. This allows the system to adapt to varying photoactive layer thicknesses, maintaining efficient charge transfer even in thicker layers through electrical control of charge neutrality and field distribution.
Solution Approach 2:
The patent changes the electrical parameters (voltage, charge neutrality) of the photoactive layer through gate control. By dynamically adjusting these parameters, the system optimizes charge transfer efficiency across different photoactive layer thicknesses, resolving the trade-off between absorption and transfer efficiency.
4Speed
If electrical shutters are used to reset photodetectors, then reset speed increases, but charge in the photoactive layer cannot be removed
Solution Approach 1:
The gate electrode serves multiple functions: it controls the transistor operation, manages charge neutrality in the photoactive layer, and performs the resetting function by removing excess charge. This multi-functionality enables both fast reset speed and complete charge removal through a single electrical mechanism.
Solution Approach 2:
The patent uses parameter changes (voltage application to gate electrode) to achieve both fast resetting and complete charge removal from the photoactive layer. By adjusting the gate voltage, the system efficiently removes charge while maintaining high reset speed, overcoming the limitation of conventional electrical shutters.
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
This approach allows for quick and reliable electrical resetting of field-effect transistors, facilitating high frame rates and effective noise reduction in light detection applications by ensuring charge neutrality even under illumination, thus enhancing the performance of photodetectors.
Implementation Method 1
The photoactive layer can be configured to donate charge carriers to the transistor channel when electromagnetic radiation is absorbed in the photoactive layer
Implementation Method 2
a gate-insulating layer between the gate electrode and the transistor channel
Data Source
Figure 1~2
Figure 3~4
Figure 5
AI summary
A photosensitive field-effect transistor which can be configured to provide an electrical response when illuminated by electromagnetic radiation incident on the transistor. The field-effect transistor has a channel (13) made from a two-dimensional material and comprises a photoactive layer (22) which can be configured to donate charge carriers to the transistor channel (13) when electromagnetic radiation is absorbed in the photoactive layer (22). The photosensitive field- effect transistor comprises a top electrode (21) which is in contact with the photoactive layer on one or more contact areas which together form a contact pattern. With a suitably patterned top electrode (21), a voltage applied to the electrode can function as an electrical shutter which can switch the photosensitive field-effect transistor between a light-sensitive state and a light-immune state.