Back-Illuminated ToF Light-Receiving Element for Low-Noise Sensing
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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 wiring layer, and a semiconductor layer with voltage application and charge detection portions covered by an insulating film, which improves charge separation efficiency and reduces noise interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
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 illumination direction from front-illuminated to back-illuminated configuration. By making the light-receiving surface the back surface of the substrate, the wiring layer is positioned on the front surface where it no longer blocks the optical path. This inversion resolves the contradiction by allowing full photoelectric conversion efficiency while maintaining wiring functionality for charge extraction.
2Reliability
If wiring capacitance is increased to secure saturation signal amount in front-illuminated CAPD sensor, then signal to noise ratio improves, but device complexity increases requiring additional transistors
Solution Approach 1:
The patent extracts the wiring layer from the light-receiving surface and relocates it to the front surface. This extraction eliminates the need for additional capacitance-compensating transistors, as the inherent wiring capacitance is sufficient when the wiring does not block light. The solution achieves high signal-to-noise ratio without increasing device complexity.
3Ease of operation
If Tap regions are arranged on the light incident surface in surface-type CAPD sensor, then signal extraction is enabled, but photoelectric conversion in inactive Tap regions creates noise reducing distance measurement accuracy
Solution Approach 1:
The patent inverts the substrate orientation so that Tap regions are positioned on the front surface rather than the light-receiving back surface. This inversion ensures that photoelectric conversion occurs primarily in the active Tap regions, eliminating noise from inactive regions and improving distance measurement accuracy while maintaining signal extraction capability.
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 back-illuminated configuration enhances pixel sensitivity, improves charge separation efficiency, and increases the accuracy of distance measurement by minimizing noise and maximizing quantum efficiency and aperture ratio.
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
each of the first voltage application portion and the second voltage application portion is covered with an insulating film in the semiconductor layer
Implementation Method 3
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
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 near the first voltage application portion, and a second charge detection portion arranged near the second voltage application portion, and each of the first voltage application portion and the second voltage application portion is covered with an insulating film in the semiconductor layer. The present technology can be applied to, for example, a light-receiving element that generates distance information by a ToF method.