Gated Photodiode Impedance Reduction via Field Plate Buffer
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Solution Overview
Problem
Existing photosensitive systems face limitations in sensitivity due to high capacitance, which counteracts the need for large pixel area and low leakage currents, particularly in medical applications requiring detection of low-level fluorescence.
Innovation Solution
A photosensitive system is designed with a gated photodiode and a low-input capacitance output buffer, where the buffer's output is connected to the photodiode's field plates, effectively reducing the photodiode's impedance and leakage, allowing for high sensitivity and low leakage without active capacitance compensation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the pixel area is increased to collect more photons, then the sensitivity is improved, but the total input capacitance increases, which degrades the sensitivity
Solution Approach 1:
The patent changes the electrical parameters of the photodiode by introducing a gated structure with adjustable gate voltage. By controlling the gate voltage, the depletion region width and junction capacitance can be dynamically adjusted, allowing the system to maintain low capacitance while collecting sufficient photons over a larger area.
Solution Approach 2:
The patent introduces dynamic control of the photodiode characteristics through the gate voltage. The gate voltage can be adjusted during operation to optimize the balance between collection area and capacitance, making the system adaptable to different detection requirements rather than being fixed.
2Measurement precision
If the total input capacitance is reduced to improve sensitivity, then the measurement precision is improved, but the leakage current control becomes more difficult
Solution Approach 1:
By changing the gate voltage parameter, the patent simultaneously controls both the capacitance and leakage current characteristics of the photodiode. The gate voltage adjustment modifies the electric field distribution, allowing optimization of both parameters together rather than treating them as conflicting requirements.
Solution Approach 2:
The patent implements feedback control through the gate voltage adjustment mechanism. The gate voltage can be dynamically adjusted based on the detected signal characteristics to maintain optimal operating conditions, compensating for variations and ensuring consistent performance.
3Measurement precision
If active capacitance compensation is used to reduce input capacitance, then the sensitivity is improved, but the device complexity increases
Solution Approach 1:
The patent extracts the capacitance control function from complex active compensation circuits and integrates it directly into the photodiode structure through the gate. This eliminates the need for external compensation components and complex feedback circuits, simplifying the overall device while maintaining the capacitance reduction benefit.
Solution Approach 2:
The patent merges the capacitance control function with the photodiode structure itself by introducing the gate. Instead of using separate compensation circuits, the capacitance control is integrated into the detection element, reducing the number of components and simplifying the device architecture.
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 design achieves an order of magnitude improvement in sensitivity, enabling sub-single photon detection and reducing total input impedance, making it competitive with complex avalanche photodiodes while maintaining affordability and low leakage.
Implementation Method 1
Incoming photons, indicated by the wavy arrow with label hv, result in a discharging of the diode
Implementation Method 2
an output buffer having an input coupled to the gated photodiode for reducing the impedance of the photodiode signal
Data Source
AI summary
Disclosed is a photosensitive system including a gated photodiode having at least one field plate and a cathode and an output buffer having an input coupled to the gated photodiode for reducing the impedance of the photodiode signal and having an output for providing the reduced impedance signal. The output is electrically connected to the at least one field plate. A device including such a photosensitive system is also disclosed.