Back-Illuminated Light-Receiving Element for ToF Sensor Sensitivity
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Solution Overview
Problem
Conventional CAPD sensors face challenges in securing a sufficient photoelectric conversion region due to wiring and control lines on the light-receiving surface, leading to deteriorated sensitivity and noise interference from external light, which affects the accuracy of distance measurement using the indirect time-of-flight method.
Innovation Solution
A light-receiving element with a back-illuminated configuration, featuring an on-chip lens, a semiconductor layer with distinct voltage application and charge detection portions, and a wiring layer with wider ground lines, which improves charge separation efficiency and reduces noise interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If wiring and control lines are arranged on the light-receiving surface of a front-illuminated CAPD sensor, then charge extraction and control functions are enabled, but the photoelectric conversion region is limited and sensitivity deteriorates
Solution Approach 1:
The patent inverts the conventional front-illuminated structure to a back-illuminated structure. By making the light-receiving surface the back surface of the substrate, the wiring layer is positioned on the front surface, allowing light to enter the photodiode conversion region without obstruction. This inversion resolves the contradiction by enabling full photoelectric conversion area while maintaining charge extraction functionality through the relocated wiring arrangement.
2Object-affected harmful factors
If wiring capacitance is reduced in a front-illuminated CAPD sensor, then external light noise is reduced, but additional transistors are needed to secure capacitance
Solution Approach 1:
By inverting to a back-illuminated structure, the patent eliminates the need for complex wiring layouts on the light-receiving surface. The wiring is positioned on the front surface where it does not block light, naturally reducing external light noise effects. This structural inversion simplifies the overall design and reduces the need for additional transistors to compensate for wiring capacitance issues.
3Ease of operation
If Tap regions are arranged on the light incident surface in a front-illuminated CAPD sensor, then signal extraction is enabled, but photoelectric conversion in Inactive Tap regions creates noise
Solution Approach 1:
The patent inverts the structure so that Tap regions are positioned on the front surface rather than the light-receiving back surface. This allows signal extraction functionality to be maintained while preventing Inactive Tap regions from being exposed to incident light, thereby eliminating the harmful photoelectric conversion noise that occurs in front-illuminated sensors.
4Measurement precision
If a larger photoelectric conversion region is secured in a front-illuminated CAPD sensor, then sensitivity improves, but wiring must be arranged to block the optical path
Solution Approach 1:
By inverting to a back-illuminated structure, the patent allows the entire substrate area to be used for photoelectric conversion without wiring obstructions. The wiring layer is positioned on the front surface, completely clearing the light-receiving back surface for maximum photoelectric conversion region area, thus resolving the contradiction between sensitivity and region area.
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 enhances pixel sensitivity, charge separation efficiency, and distance-measuring characteristics by minimizing noise and maximizing quantum efficiency and aperture ratio, thereby improving the overall performance of CAPD sensors.
Implementation Method 1
a sensor capable of distributing signal charges in different regions at a high speed, the signal charges being obtained by receiving light hitting and reflected at an object
Implementation Method 2
a sensor capable of distributing signal charges in different regions at a high speed, the signal charges being obtained by receiving light hitting and reflected at an object
Data Source
AI summary
The present technology relates to a light-receiving element and a distance-measuring module for enabling improvement of characteristics. A light-receiving element includes an on-chip lens, a wiring layer, and a semiconductor layer arranged between the on-chip lens and the wiring layer, the semiconductor layer includes a first voltage application portion to which a first voltage is applied, a second voltage application portion to which a second voltage different from the first voltage is applied, a first charge detection portion arranged around the first voltage application portion, and a second charge detection portion arranged around the second voltage application portion, and the wiring layer includes at least one ground line having a wider line width than a power supply line. The present technology can be applied to, for example, a light-receiving element that generates distance information by a ToF method.