SPAD Sensor Layout With Buried Quench Resistor for Higher Fill Factor
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Solution Overview
Problem
Conventional single-photon avalanche diodes (SPADs) face challenges in achieving high fill factor and photon detection efficiency due to the integration of surface polysilicon quenching resistors, which result in low fill factor and photon detection efficiency, and require suitable quenching electronics to prevent device damage from avalanche currents.
Innovation Solution
A sensor design incorporating a substrate with a first semiconductor layer, a second semiconductor layer, and a buried insulator layer, where a photodiode is formed in the first layer and a quenching resistive element is integrated in the second layer, separated by the buried insulator, allowing for a smaller footprint and higher fill factor, and adjustable quenching resistance to enhance photon detection efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If surface polysilicon quenching resistor is integrated in conventional SPAD, then quenching function is achieved, but fill factor and photon detection efficiency are reduced
Solution Approach 1:
The patent moves the quenching resistor from the surface plane to a lower layer beneath the photodiode, utilizing the vertical dimension. This is achieved by forming the quenching resistor in a first semiconductor layer and positioning the photodiode in a second semiconductor layer above it, separated by an insulator layer. This dimensional reorganization allows the quenching function to be maintained while eliminating the footprint occupation on the light-receiving surface, thereby maximizing fill factor and photon detection efficiency.
2Reliability
If surface polysilicon quenching resistor is used, then avalanche current quenching is enabled, but device footprint increases
Solution Approach 1:
The patent relocates the quenching resistor to a lower layer in the vertical stack, specifically in the first semiconductor layer beneath the photodiode. This vertical integration allows the quenching resistor to perform its function without occupying lateral space on the device surface. The insulator layer between the two layers provides electrical isolation while maintaining the series connection for quenching, thus reducing device footprint while preserving avalanche current quenching capability.
3Area of stationary object
If backside illumination is implemented to achieve high fill factor, then photon detection efficiency is improved, but device structure complexity increases
Solution Approach 1:
The patent achieves high fill factor through vertical integration rather than backside illumination. By stacking the quenching resistor below the photodiode in separate semiconductor layers, the entire active area of the photodiode remains exposed to light from the front surface. This front-side illumination approach maintains simple device structure while achieving maximum fill factor, avoiding the complexity of backside illumination processing.
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 solution achieves a higher fill factor and photon detection efficiency by integrating the photodiode and quenching resistive element in separate semiconductor layers, enabling front side illumination and reducing the footprint of the sensor, while effectively quenching avalanche currents to prevent device damage.
Implementation Method 1
Single-photon avalanche diodes (SPADs, or Geiger mode avalanche diodes), capable of detecting and time-stamping single optical photons
Implementation Method 2
SPADs are based on a p-n junction, which is reverse biased at an operating voltage Vop that exceeds a breakdown voltage VB of the junction. At this bias, a single charge carrier injected into the depletion layer can trigger a self-sustaining avalanche, giving rise to a macroscopic level current.
Implementation Method 3
the avalanche current must be quenched to avoid damaging the device by overheating. Accordingly, the SPAD usually needs suitable quenching electronics, e.g., a ballast quench resistor having a resistance over 100 kΩ, to interrupt the avalanche process right after the avalanche build-up by promptly lowering the reverse bias of the junction below the breakdown voltage.
Data Source
AI summary
A sensor may be provided, including a substrate having a first semiconductor layer, a second semiconductor layer, and a buried insulator layer arranged between the first semiconductor layer and the second semiconductor layer. The sensor may further include a photodiode arranged in the first semiconductor layer; and a quenching resistive element electrically connected in series with the photodiode. The quenching resistive element is arranged in the second semiconductor layer, and the quenching resistive element is arranged over the photodiode but separated from the photodiode by the buried insulator layer.