Overlaid PIN Photodiode Pixels for Faster TOF Distance Detection
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Solution Overview
Problem
Conventional 3D image sensors based on time-of-flight (TOF) distance measuring techniques face challenges in achieving high accuracy due to slow electron movement in photodiodes, which affects the speed and precision of distance measurement.
Innovation Solution
Incorporating a PIN diode that overlaps with the photodiode to enhance the electric field, thereby increasing the speed of electron movement in the photodiodes, using a semiconductor substrate with a pixel array and a floating diffusion region to collect charges.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a conventional photodiode structure is used in TOF sensors, then the device complexity is low, but the electron movement speed is slow which reduces measurement accuracy
Solution Approach 1:
The patent combines a photodiode with an overlaid PIN diode structure to create a composite semiconductor device. The PIN diode is disposed over the photodiode with its intrinsic region positioned between the P-type and N-type regions, forming a composite structure that leverages the charge carrier generation capabilities of the photodiode and the high-speed electron transport properties of the PIN diode's intrinsic region, thereby resolving the contradiction between measurement precision and electron movement speed
Solution Approach 2:
The patent modifies the electrical parameters of the photodiode by overlaying it with a PIN diode structure. The PIN diode introduces a high-resistance intrinsic region that creates strong electric fields, which significantly alter the charge carrier drift velocity and reduce electron transit time. This parameter change transforms the photodiode's electrical characteristics to achieve faster electron movement while maintaining detection accuracy
2Speed
If the photodiode structure is modified to increase electron speed, then the measurement accuracy improves, but the device complexity increases
Solution Approach 1:
The patent merges the photodiode and PIN diode into a single integrated pixel structure where the PIN diode is disposed directly over the photodiode. This merging approach combines the light-sensing function of the photodiode with the high-speed electron transport function of the PIN diode in one unified device, achieving fast electron movement without requiring separate components or complex multi-stage processing circuits
3Speed
If a PIN diode is added to the photodiode structure, then the electron movement speed increases, but the manufacturing complexity increases
Solution Approach 1:
The overlaid PIN diode structure serves multiple functions simultaneously: it acts as a charge carrier acceleration region, provides electrical isolation, and maintains optical transparency. This multi-functionality reduces the need for additional specialized components or complex fabrication steps, as the same PIN diode structure performs multiple roles that would otherwise require separate elements
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 implementation of a PIN diode improves the speed of electron movement, enhancing the accuracy of the time-of-flight distance measuring system by reducing errors in estimating flight time.
Implementation Method 1
a photodiode, disposed in the semiconductor substrate and adjacent to the first surface, wherein the photodiode is configured to sense light to generate charges
Implementation Method 2
the light sensor and the related time-of-flight distance measuring system disclosed in the present application uses a PIN diode to increase the speed that electrons move in the photodiodes of the pixels
Data Source
AI summary
This application discloses a light sensor and a related time-of-flight distance measuring system. The light sensor includes a semiconductor substrate, having a first surface and a second surface; a photodiode, disposed in the semiconductor substrate and adjacent to the first surface, wherein the photodiode is configured to sense light to generate charges; a first floating diffusion region, disposed in the semiconductor substrate and adjacent to the first surface, and configured to collect charges during a sampling operation; a gate, disposed on the semiconductor substrate, and configured to selectively control the charges to enter the first floating diffusion region; and PIN diode, disposed on the photodiode, wherein the PIN diode at least partially overlaps with the photodiode, when viewed from a top view.