Actively Cooled Sensor Array With Thermal Barrier for Dark-Current Noise
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
High-resolution CMOS image sensors face significant dark-current noise, which limits their ability to perform single-photon counting, especially at varying ambient temperatures, as dark-current noise scales with pixel area and is exacerbated by thermal generation of electron-hole pairs.
Innovation Solution
The implementation of an actively cooled image sensor architecture, where a thermal-barrier zone separates the sensor array from the readout circuit, and a nanoscale Peltier-effect cooler is used to maintain the sensor array at a low temperature (10-20°C), reducing dark-current noise by minimizing indirect heating and cooling load.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the sensor array is cooled to reduce dark-current noise, then measurement precision is improved, but device complexity increases due to the need for active cooling mechanisms
Solution Approach 1:
The image sensor is divided into functionally independent zones: a first region containing the sensor array that requires cooling, and a second region containing the readout circuit that operates at higher temperatures. This segmentation allows each zone to be optimized for its specific temperature requirements, enabling single-photon counting capability in the sensor array while avoiding the complexity of cooling the entire device.
Solution Approach 2:
Different regions of the image sensor are assigned different thermal characteristics. The first region (sensor array) is designed with thermal isolation and active cooling to maintain low temperatures for high-precision photon detection, while the second region (readout circuit) is allowed to operate at higher temperatures. This local differentiation of thermal properties resolves the contradiction by applying cooling only where measurement precision is critical.
2Object-affected harmful factors
If the sensor array is actively cooled, then dark-current noise is reduced, but energy consumption increases due to the cooling load
Solution Approach 1:
The cooling system is segmented to cool only the first region (sensor array) that is sensitive to dark-current noise, while the second region (readout circuit) remains uncooled. This selective cooling approach minimizes energy consumption by applying active cooling only where it is necessary to reduce harmful thermal effects, rather than cooling the entire device.
Solution Approach 2:
A thermal-barrier zone is introduced as an intermediary structure between the first region (sensor array) and the second region (readout circuit). This thermal barrier isolates the sensor array thermally, allowing it to be cooled independently with minimal energy input, while preventing the cooling load from propagating to the readout circuit. The thermal-barrier zone acts as a mediator that enables localized cooling with reduced energy consumption.
3Temperature
If the sensor array is isolated thermally from the readout circuit, then temperature control is improved, but manufacturing precision becomes more difficult due to trench formation requirements
Solution Approach 1:
The substrate is segmented into distinct regions with a thermal-barrier zone separating the first region (sensor array) from the second region (readout circuit). This segmentation is achieved through trench formation that creates physical and thermal separation. The manufacturing process is designed to accommodate this segmentation by forming trenches with controlled depth and alignment, balancing the need for temperature control with manufacturing feasibility.
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 effectively reduces dark-current noise, enabling single-photon counting capabilities in low-light conditions and for applications like night vision and time-of-flight depth imaging, while maintaining other components at higher temperatures without increasing dark current.
Implementation Method 1
a nanoscale Peltier-effect cooler is used to maintain the sensor array at a low temperature (10-20°C), reducing dark-current noise by minimizing indirect heating and cooling load
Implementation Method 2
a thermal-barrier zone separates the sensor array from the readout circuit
Data Source
AI summary
A method for fabricating an image sensor comprises: forming an array of sensor elements on a sensor-wafer substrate; forming a readout circuit on the sensor-wafer substrate; forming a plurality of signal lines between the array of sensor elements and the readout circuit; forming a solid-state cooler between the array of sensor elements and the readout circuit; bonding a carrier-wafer substrate to an epitaxial structure of the sensor-wafer substrate; etching the carrier-wafer substrate in the thermal-barrier zone to form a carrier-wafer trench between the array of sensor elements and the readout circuit; reducing the thickness of the sensor-wafer substrate; and etching the sensor-wafer substrate in the thermal-barrier zone to form a sensor-wafer trench between the array of sensor elements and the readout circuit.