Image Sensor Photo Gate Segmentation for Fluorescence Lifetime Imaging
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Solution Overview
Problem
Existing image sensors for fluorescence lifetime imaging and time-of-flight measurements face challenges in achieving high demodulation frequencies while maintaining high fill factor, low power consumption, and efficient electron drift, often requiring complex and costly micro-optical elements or high power dissipation.
Innovation Solution
The solution involves splitting the photo gate into three sub-gates, applying a reduced clocking voltage to the outer photogates, and maintaining a DC-voltage on the middle photo gate, which increases the local drift field and allows for larger pixel sizes and reduced power consumption, enabling higher demodulation frequencies and lower power usage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a high demodulation frequency is achieved by increasing the voltage swing on toggle gates, then the electron drift time is reduced, but the power consumption increases significantly
Solution Approach 1:
The photo gate is divided into multiple segments (first photo gate and second photo gate) that can be independently controlled with different voltage swings. This segmentation allows the invention to apply reduced voltage swing to one segment while maintaining adequate electron drift through the combined effect of both segments and the toggle gates, thereby reducing overall power consumption while preserving electron drift performance.
2Speed
If the length of the photo gate is reduced to accommodate high demodulation frequency, then the electron drift time is shortened, but the fill factor decreases
Solution Approach 1:
By dividing the photo gate into multiple segments, the invention can extend the total photo gate length across multiple segments while maintaining short drift distances within each segment. This allows the fill factor to be increased through longer overall photo gate coverage while the electron drift time remains short due to the segmented structure and associated electric fields.
Solution Approach 2:
Different regions of the photo gate (different segments) can have different voltage characteristics optimized for their specific function. The segmented structure allows local optimization where each segment contributes to the overall photo collection area while maintaining appropriate electric field conditions for rapid electron drift in its region.
3Measurement precision
If micro-optical elements are added to distribute light evenly, then the measurement accuracy improves, but the device complexity and cost increase
Solution Approach 1:
The invention removes the micro-optical elements from the system while achieving the same measurement precision through an alternative approach. By using the segmented photo gate structure with independent voltage control, the system can process light from different spatial regions separately and combine the information, achieving accurate phase measurement without requiring micro-optical elements for light distribution.
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
This approach enables higher demodulation frequencies, larger pixel sizes for increased light sensitivity, and significantly reduced power consumption, making it advantageous for both CCD and CMOS image sensors.
Implementation Method 1
The maximum modulation frequency is determined to a large extend by the electric fields that that drive the electrons to the collection well
Implementation Method 2
photo-generated electrons are generated in a photo gate region
Data Source
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AI summary
The invention relates to an image sensor for fluorescent lifetime imaging. The image sensor comprises: an array of pixel regions (1'), each pixel region (1') having an aperture for receiving light from a modulated light source in an integration phase of the pixel region (1'), each pixel region (1') comprising a photo gate region (PHR) being embedded on opposite sides by two storage regions (120,120'), and further comprising a respective toggle gate (110,110') between the photo gate region (PHR) and each respective one of the storage regions (120, 120', 121, 121'). The photo gate region (PHR) comprises at least three photo gates (100-1, 100-2, 100-3) arranged parallel to each other and parallel to the toggle gates (110,110'), wherein, in operational use, at least outer ones of the photo gates (100-1, 100-3) carry a photo gate signal, and wherein respective photo gate signals are modulated with a photo voltage swing and in synchronicity with its nearest toggle gate (110,110'), wherein the photo voltage swing is lower than the toggle voltage swing, In operational use during the integration phase, one of the remaining middle photo gates (100-2) in the photo gate region (PHR) is not modulated, but provided with a pre-defined DC-voltage, wherein the pre-defined DC-voltage lies in between the extremes of the respective photo gate signals. The invention provides a solution to the problems in the prior art, which may be exploited towards higher operating frequencies, lower power, and/or higher light sensitivity.