Silicon Photon Detector Using Floating Body SOI Transistor
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Solution Overview
Problem
Conventional photon detectors, particularly silicon-based and CMOS detectors, are inefficient at converting low-energy light, slow, space-intensive, and unable to detect mid-infrared light, limiting their integration with existing integrated circuits and telecommunications applications.
Innovation Solution
A compact silicon-based optical detector using a semiconductor-on-insulator (SOI) transistor with a floating body that traps excess carriers from detected light, enhancing drain current and enabling efficient conversion of photons to electrical signals, capable of detecting visible and mid-infrared light up to 1500 nm, fabricated using standard CMOS processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional silicon-based light detectors are used, then the detector can be integrated with existing CMOS fabrication processes, but the detection efficiency is very low for light with energy below 1.1 eV (wavelength greater than 1050 nm) due to the indirect bandgap of silicon
Solution Approach 1:
The patent changes the detection parameter by using a different physical mechanism (photoconductive effect in highly doped silicon) rather than relying on the indirect bandgap limitation. By heavily doping the silicon to create a high carrier concentration, the material becomes transparent to infrared light while maintaining efficient detection through free carrier absorption, thus resolving the contradiction between manufacturability and detection efficiency.
Solution Approach 2:
The patent substitutes the conventional photovoltaic or photodiode mechanism with a photoconductive detection mechanism using highly doped silicon. This replacement allows the detector to operate efficiently at wavelengths beyond 1050 nm while remaining compatible with standard silicon fabrication processes, thereby resolving the efficiency limitation without sacrificing ease of manufacture.
2Device complexity
If conventional CCD, CMOS or BJT light detectors are used, then the detector structure is simple and compatible with standard fabrication, but the detection speed is slow due to intrinsic RC times required to charge and discharge
Solution Approach 1:
The patent changes the electrical parameters by using a field-effect transistor configuration with a floating body that accumulates photo-generated carriers. This approach eliminates the need for slow charge/discharge cycles of conventional capacitive detectors, achieving fast detection speed while maintaining a simple structure that is compatible with standard CMOS fabrication.
Solution Approach 2:
The patent introduces a floating body region in the MOSFET structure as an intermediary that temporarily stores photo-generated carriers. This floating body acts as a natural integration node that can be rapidly read out through the transistor channel, enabling fast detection speed without requiring large capacitive structures that would slow down the response.
3Reliability
If conventional light detectors with large active area are used, then the detector can capture more light, but the device occupies too much space for integration
Solution Approach 1:
The patent changes the optical parameter by using highly doped silicon that exhibits strong free carrier absorption in the infrared range. This allows the detector to maintain high quantum efficiency with a much smaller active area compared to conventional detectors, thereby resolving the contradiction between light capture capability and device area.
Solution Approach 2:
The patent employs a composite structure combining highly doped silicon region with a MOSFET configuration. The heavily doped silicon provides enhanced infrared absorption in a compact volume, while the MOSFET structure provides efficient carrier collection and signal amplification, achieving high light capture capability in a small footprint suitable for integration.
4Adaptability or versatility
If detectors are designed to detect mid-infrared light, then the detector can extend into new wavelength ranges, but conventional detectors cannot detect light with wavelength above 1100 nm due to zero efficiency
Solution Approach 1:
The patent substitutes the conventional bandgap-based detection mechanism with a free carrier absorption mechanism in highly doped silicon. This substitution enables detection of mid-infrared light up to 1500 nm and beyond, extending the wavelength range while maintaining high detection efficiency that is incompatible with conventional detector designs.
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 improved sensitivity and gain in photon detection, enabling efficient conversion of mid-infrared light to electrical signals, reducing threshold voltage, and enhancing detection speed through parallel architectures and mode-switching transistors.
Implementation Method 1
the floating body region traps excess carriers from the first light source when a first relatively lower reference voltage is applied to the gate electrode and source and drain regions so that excess charges can be detected as enhanced drain current
Implementation Method 2
The excess carriers in the body (holes for NMOS and electrons for PMOS) will remain in the body, but will electrostatically couple to the transistor channel, which works to reduce the threshold voltage and hence enhance drain current in read mode
Implementation Method 3
In this way, the optical detector converts photons to an electrical signal with gain
Data Source
AI summary
A silicon photon detector device and methodology are provided for detecting incident photons in a partially depleted floating body SOI field-effect transistor (310) which traps charges created by visible and mid infrared light in a floating body region (304) when the silicon photon detector is configured in a detect mode, and then measures or reads the resulting enhanced drain current with a current detector in a read mode.