On-Chip Lens APD Sensor Layout for Lower ToF Light Loss
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Solution Overview
Problem
Existing distance measurement apparatuses using the Time of Flight (ToF) method face challenges in improving the sensitivity of their sensors, particularly those employing avalanche photodiodes (APDs).
Innovation Solution
The proposed solution involves a sensor design that includes a semiconductor substrate with an APD, an on-chip lens, a first reflective member on the on-chip lens, and a wiring layer with a second reflective member. This configuration allows for efficient reflection and re-entry of light into the APD, enhancing sensitivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a single reflective member is used in the sensor, then the structure is simpler, but light loss occurs and sensitivity is insufficient
Solution Approach 1:
The reflective function is segmented into two separate reflective members: a first reflective member positioned to reflect incident light toward the APD, and a second reflective member positioned to reflect transmitted light back through the semiconductor substrate. This segmentation allows each reflective member to perform a specific function in the light path, reducing overall light loss while maintaining manageable structural complexity through modular design.
Solution Approach 2:
The light reflection process is extended into a multi-dimensional path by adding the second reflective member on the opposite side of the semiconductor substrate. Instead of a single-plane reflection, the system creates a three-dimensional light path where light can be reflected from both the front surface (first reflective member) and the back surface (second reflective member), effectively utilizing the thickness dimension of the substrate to reduce light loss.
2Reliability
If light is allowed to pass through the semiconductor substrate without reflection, then the structure is simpler, but detection sensitivity is reduced
Solution Approach 1:
The second reflective member is positioned in advance on the second surface of the semiconductor substrate to preemptively reflect transmitted light back through the substrate toward the APD. This preliminary positioning ensures that light which passes through the substrate is not lost but is instead redirected to contribute to the detection signal, thereby improving detection sensitivity before light loss can occur.
Solution Approach 2:
The second reflective member creates a feedback mechanism where light transmitted through the semiconductor substrate is reflected back and re-enters the APD from the rear side. This feedback loop allows the APD to receive additional photons that would otherwise be lost, enhancing the overall detection sensitivity and signal strength without requiring a fundamentally different detection mechanism.
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 described configuration significantly improves the sensitivity of the sensor by ensuring that light reflected by the second reflective member is effectively reflected back into the APD, reducing light loss and enhancing detection capabilities.
Implementation Method 1
the first reflective member is provided that reflects light reflected by the second reflective member
Implementation Method 2
The sensor includes the APD for each pixel... an avalanche photodiode... light reflected by the target is received by a sensor
Implementation Method 3
an on-chip lens provided on side of the first surface of the semiconductor substrate
Data Source
AI summary
A sensor including: a semiconductor substrate (41) having a first surface (S1) and a second surface (S2) opposed to each other, and including an avalanche photodiode; an on-chip lens (71) provided on side of the first surface (S1) of the semiconductor substrate (41); a first reflective member (73) provided on the on-chip lens (71); and a wiring layer (42) provided on side of the second surface (S2) of the semiconductor substrate (41), and including a second reflective member (104).