Heterojunction Bipolar Transistor Thermal Sensor for 1/f Noise Reduction
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Solution Overview
Problem
CMOS sensors face challenges with 1/f noise, particularly at low frequencies, which are difficult to filter out using frequency-based techniques, and there is a need for highly sensitive thermal sensors.
Innovation Solution
A sensing device incorporating a heterojunction bipolar transistor with a base made of Silicon Germanium, thermally isolated from a bulk using a MEMS or NEMS process, and coupled to a CMOS readout circuit to detect temperature changes caused by electromagnetic radiation, allowing for the conversion of infrared radiation to heat and processing of detection signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If CMOS sensors are used for detection, then the device can be manufactured with standard CMOS processes, but the sensor suffers from high 1/f noise at low frequencies that is difficult to filter
Solution Approach 1:
The patent introduces a heterojunction bipolar transistor as an intermediary sensing element between the incident radiation and the CMOS readout circuit. This bipolar transistor converts the radiation-induced temperature changes into electrical signals that can be read out by the CMOS circuit, thereby avoiding direct use of CMOS pixels for sensing and eliminating the 1/f noise problem while maintaining CMOS manufacturing compatibility
Solution Approach 2:
The patent changes the sensing mechanism from direct electrical detection in CMOS to thermal detection using a bipolar transistor. By operating the bipolar transistor in a configuration where collector current is exponentially dependent on base-emitter voltage and temperature, the system transforms temperature changes into measurable electrical signals with high sensitivity and low noise
2Measurement precision
If the heterojunction bipolar transistor is thermally isolated from the bulk, then the sensitivity to electromagnetic radiation is enhanced, but the mechanical support and thermal management become more complex
Solution Approach 1:
The patent segments the device into distinct functional regions: a suspended sensing area where the heterojunction bipolar transistor is thermally isolated from the bulk substrate, and a support structure that provides mechanical anchoring. This segmentation allows the sensing region to be thermally isolated for high sensitivity while the support structure handles mechanical and thermal management functions
Solution Approach 2:
The patent transitions from a planar device architecture to a three-dimensional suspended structure. The heterojunction bipolar transistor is positioned above the bulk substrate with thermal isolation in the vertical dimension, while electrical connections are maintained through suspended conductors. This dimensional change enables thermal isolation without completely separating the device from its support structure
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 effectively reduces 1/f noise and enhances sensitivity, enabling the detection of electromagnetic radiation while maintaining thermal isolation and mechanical support, thus addressing the need for improved thermal sensors.
Implementation Method 1
The heterojunction bipolar transistor may be configured to convert infrared radiation to heat
Implementation Method 2
generating, by the heterojunction bipolar transistor, detection signals responsive to the temperature of at least portion of the heterojunction bipolar transistor
Data Source
AI summary
A method and a sensing device are provided. The sensing device may include a readout circuit, a bulk, a holding element and a heterojunction bipolar transistor; wherein heterojunction bipolar transistor is configured to generate detection signals responsive to a temperature of at least a portion of the heterojunction bipolar transistor; wherein the holding element is configured to support the heterojunction bipolar transistor; wherein the heterojunction bipolar transistor is thermally isolated from the bulk; wherein the readout circuit is electrically coupled to the heterojunction bipolar transistor; and wherein the readout circuit is configured to receive the detection signals and to process the detection signals to provide information about electromagnetic radiation that affected the temperature of the at least portion of the heterojunction bipolar transistor.