Optical Sensor Doping Region Prevents Depletion
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Solution Overview
Problem
Optical sensors employing photogate structures face limitations due to high dark current, signal-to-noise ratio limitations, and challenges in redirecting photo-generated charge carriers, which are exacerbated by temperature increases and the need for complex signal analysis and expensive doping processes.
Innovation Solution
An optical sensor device with a semiconductor substrate featuring a conversion region, a read-out node, and a control electrode separated by an isolating material, along with a doping region of higher concentration than the conversion region, which extends into the substrate and prevents depletion, enabling an electric modulation field for demodulating electromagnetic signals and improving signal-to-noise ratio.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If photogates are located adjacent to a depleted silicon region to redirect photo-generated charge carriers, then charge carrier redirection is achieved, but dark current increases exponentially at higher temperatures
Solution Approach 1:
The patent changes the doping concentration parameter in the semiconductor substrate, creating a heavily doped region (1000 times higher than minimum) to prevent depletion and reduce dark current generation while maintaining charge carrier redirection capability
Solution Approach 2:
The patent extracts the control electrode from direct contact with the semiconductor substrate by introducing an isolating material layer, thereby eliminating the depletion region at the electrode-substrate interface that causes dark current
2Reliability
If a depleted silicon region is used to shift photo-generated charge carriers, then charge carrier shifting is achieved, but the depth of the absorption region is limited
Solution Approach 1:
The patent changes the doping concentration parameter to create a heavily doped region that prevents depletion, allowing the absorption region to extend deeper into the semiconductor substrate while maintaining effective charge carrier shifting through the modified electric field distribution
3Manufacturing precision
If expensive processes and tools are used to control doping concentration in the bulk, then doping precision is improved, but manufacturing cost increases
Solution Approach 1:
The patent applies local quality by creating a heavily doped region only in specific areas where control electrodes are located, rather than uniformly doping the entire bulk, thereby reducing the need for expensive bulk doping control processes while achieving the desired electrical field modulation
4Reliability
If photogates are located in the optical path to redirect charge carriers, then charge carrier redirection is achieved, but optical absorption or reflection occurs especially at short wavelengths
Solution Approach 1:
The patent extracts the control electrode from the optical path by introducing an isolating material layer between the electrode and the semiconductor substrate, eliminating optical absorption and reflection by the electrode while maintaining charge carrier redirection through the electric field effect
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 enhances the conversion of optical signals into electrical signals, achieving faster measurement and improved signal quality by preventing charge carrier depletion and reducing noise, thus overcoming the limitations of current optical sensor designs.
Implementation Method 1
The electric modulation field (also referred to as potential distribution) may be used to demodulate an inbound electromagnetic signal such as light from infrared to ultraviolet wavelengths. The electric modulation field may be caused by the control electrode, capacitively inducing or providing a current to the semiconductor substrate.
Implementation Method 2
a conversion region to convert an electromagnetic signal into photo-generated charge carriers
Implementation Method 3
Since the doping region comprises a large number of charge carriers compared to the charge carriers present in the semiconductor substrate, a depletion of the semiconductor substrate adjacent to the control electrode is prevented. Therefore, an alternating current in the doping region provides a drift field in the semiconductor substrate
Data Source
AI summary
An optical sensor device comprising a conversion region to convert an electromagnetic signal into photo-generated charge carriers is shown. The optical sensor device comprises a read-out node configured to read-out the photo-generated charge carriers and a control electrode which is separated by an isolating material from the conversion region. Furthermore, the optical sensor device comprises a doping region in the semiconductor substrate between the control electrode and the conversion region, wherein the doping region comprises a higher doping concentration compared to a minimum doping concentration of the conversion region, wherein the doping concentration is at least 1000 times higher than the minimum doping concentration of the conversion region and wherein the doping region extends into the semiconductor substrate. Moreover, a projection of the control electrode towards the conversion region overlaps the doping region or is located in the doping region. Embodiments show the optical sensor device as a time-of-flight sensor.