MicroLED-Based ToF Sensors With Monolithic CMOS Detection
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Solution Overview
Problem
Existing optical time of flight (ToF) systems face challenges in cost, complexity, and compatibility issues due to the use of VCSELs and SPADs, which are expensive, complex, and not fully compatible with CMOS processes, limiting their application in low-cost, high-performance devices.
Innovation Solution
Integration of microLEDs with CMOS-compatible detectors, utilizing a p-doped region, n-doped region, and active region with quantum wells, and photodetectors on a silicon chip, enabling high-speed, low-cost ToF sensors with improved signal-to-noise ratio and scalability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If VCSELs are used as light sources, then high speed and fast response are achieved, but device complexity and manufacturing cost increase due to multi-layer mirrors and complex structure
Solution Approach 1:
The patent replaces expensive, complex VCSELs with simpler, cheaper LEDs that can be manufactured using standard CMOS processes. While LEDs traditionally have slower response times, the patent uses modern high-speed LEDs with optimized structures (including photonic crystal structures) to achieve sufficient speed for ToF applications at a fraction of the cost and complexity of VCSELs
Solution Approach 2:
The patent changes the operating parameters and structure of LEDs to improve their response speed. This includes using high-bandwidth LED structures, optimizing the photonic crystal cavity design, and operating the LEDs in pulsed modes to achieve fast rise and fall times suitable for time-of-flight measurements, thereby resolving the speed limitation while maintaining simplicity
2Measurement precision
If SPADs are used as detectors, then highest sensitivity is achieved, but compatibility with CMOS processes is lost requiring complex multi-chip assemblies
Solution Approach 1:
The patent merges the detector functionality directly into the CMOS imaging sensor chip, eliminating the need for separate SPAD chips and complex multi-chip assemblies. The ToF measurement capabilities are integrated into the standard CMOS image sensor, allowing sensitivity measurements to be performed using the existing pixel structure and readout circuitry, thereby reducing device complexity while maintaining measurement precision
Solution Approach 2:
The patent makes the CMOS image sensor perform multiple functions: standard color imaging and time-of-flight depth measurement. By utilizing the existing pixel array and readout circuitry for both imaging and ToF measurements, the system achieves detector sensitivity without requiring dedicated SPAD hardware, thus avoiding the complexity of multi-chip assemblies while maintaining universal functionality
3Power
If edge-emitting lasers are used, then higher optical power is generated, but power consumption and device size increase
Solution Approach 1:
The patent optimizes LED operating parameters including drive current, pulse width, and duty cycle to achieve sufficient optical output power for ToF measurements. By using high-efficiency LED structures and optimized drive circuits, the system generates adequate optical power with lower overall power consumption compared to edge-emitting lasers, which require continuous high current operation to achieve similar output levels
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 provides high-resolution ToF sensors with reduced cost and complexity, utilizing microLEDs for fast light sources and CMOS-compatible detectors, enabling scalable arrays for diverse applications.
Implementation Method 1
a light emitting diode (LED) having a p-doped region, an n-doped region, and an active region with doping... the active region comprises at least two quantum wells separated by a barrier, and doping of the active region comprises doping of the barrier
Implementation Method 2
a photodetector in a silicon chip... Information from each pixel of the detector may be used to compute the local time delay of the reflected light
Data Source
AI summary
A time of flight system may include one or more microLEDs and a photodetector monolithically integrated with integrated circuitry of the time of flight system. The microLEDs may be doped to provide increased speed of operation.