Stacked Avalanche Photodiode Pixel Circuit for High Reverse Bias
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Solution Overview
Problem
Existing photoelectric conversion apparatuses face challenges in achieving both high performance and miniaturization of pixels, particularly when increasing the reverse bias applied to avalanche photodiodes, which requires large element sizes for high-voltage transistors.
Innovation Solution
The proposed solution involves a photoelectric conversion apparatus with a stacked substrate configuration, including an avalanche photodiode on a first semiconductor layer, a first resistive element connected to the avalanche photodiode, a waveform shaping portion on a second semiconductor layer, and a second resistive element connected to the avalanche photodiode, the waveform shaping portion, and the first resistive element.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a high-voltage transistor with large element size is used to increase reverse bias applied to avalanche photodiode, then photoelectric conversion performance is improved, but pixel area increases
Solution Approach 1:
The pixel circuit is divided into multiple functional blocks distributed across two substrates: the first substrate contains the avalanche photodiode and first resistive element, while the second substrate contains the waveform shaping portion and second resistive element. This segmentation allows each component to be optimized independently, enabling high reverse bias operation without requiring a single large high-voltage transistor on one substrate.
Solution Approach 2:
The invention transitions from a planar single-substrate layout to a three-dimensional stacked multi-substrate configuration. By stacking the first substrate (with avalanche photodiode) and second substrate (with waveform shaping portion) vertically, the patent achieves high photoelectric conversion performance through effective use of reverse bias while maintaining compact pixel area footprint.
2Measurement precision
If reverse bias is increased to improve avalanche photodiode performance, then signal detection capability is improved, but dielectric breakdown risk increases
Solution Approach 1:
The waveform shaping portion is designed with controlled impedance and signal conditioning capabilities that prepare and condition signals before they reach subsequent circuit stages. This preliminary signal shaping prevents voltage spikes and transient overvoltages that could cause dielectric breakdown, allowing the system to operate at high reverse bias levels safely.
Solution Approach 2:
The first and second resistive elements act as intermediary components between the avalanche photodiode and the waveform shaping portion. These resistive elements serve as voltage dividers and current limiters, mediating the high reverse bias voltage to prevent direct exposure of sensitive circuit elements to excessive voltage levels that would cause dielectric breakdown.
3Reliability
If signal amplitude is reduced to prevent dielectric breakdown, then device reliability is improved, but signal-to-noise ratio deteriorates
Solution Approach 1:
The patent replaces traditional high-voltage transistor-based signal conditioning with a resistive divider and waveform shaping approach. The second resistive element and waveform shaping portion work together to condition signals with controlled impedance matching, achieving signal amplitude reduction without the need for large high-voltage transistors that would degrade signal quality through parasitic effects.
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 configuration allows for the achievement of high performance and miniaturization of pixels by reducing the signal amplitude and preventing dielectric breakdown, while also enabling area reduction of the pixel circuit.
Implementation Method 1
a photoelectric conversion apparatus including a first substrate including a first semiconductor layer and a first wiring structure stacked on the first semiconductor layer, and a second substrate including a second semiconductor layer and a second wiring structure stacked on the second semiconductor layer, includes an avalanche photodiode arranged on the first semiconductor layer
Data Source
AI summary
A photoelectric conversion apparatus including a first substrate including a first semiconductor layer and a first wiring structure stacked on the first semiconductor layer, and a second substrate including a second semiconductor layer and a second wiring structure stacked on the second semiconductor layer, includes an avalanche photodiode arranged on the first semiconductor layer, a first resistive element arranged on the first substrate and connected to the avalanche photodiode, a waveform shaping portion arranged on the second semiconductor layer and configured to shape an output signal of the avalanche photodiode, and a second resistive element arranged on the first substrate and connected to the avalanche photodiode, the waveform shaping portion, and the first resistive element.