CT Image Sensor with Integrated Photodiodes and ADCs
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Solution Overview
Problem
Conventional image sensors for computed tomography (CT) applications are complex and costly due to the use of two bonded semiconductor substrates and through silicon vias, which increases manufacturing complexity and reduces resolution.
Innovation Solution
An image sensor design featuring a semiconductor substrate with photodiodes and analog-to-digital converters (ADCs) integrated on the same substrate, using a CMOS manufacturing process with buried electrical connections to minimize surface area usage and incorporate X-ray radiation-tolerant photodiodes with a doped surface region for reduced leakage currents, and a wavelength conversion layer for improved radiation detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If two bonded semiconductor substrates with through silicon vias are used, then electrical connections between photodiodes and ADCs are achieved, but manufacturing complexity and cost increase
Solution Approach 1:
The patent merges the photodiodes and ADCs onto a single semiconductor substrate, eliminating the need for bonding two separate substrates together. This integration approach maintains electrical connection reliability while significantly reducing manufacturing complexity by removing the wafer bonding and through silicon via formation processes.
Solution Approach 2:
The patent extracts the ADCs from the second substrate and places them directly on the first substrate alongside the photodiodes. This extraction eliminates the need for complex through silicon via connections while maintaining the functional separation between photodetection and conversion operations.
2Ease of manufacture
If ADCs are placed at the front side of the substrate, then electrical connections are simplified, but sensor resolution is reduced due to reduced photodiode area
Solution Approach 1:
The patent applies local quality by placing ADCs in a specific region (second region) separated from the photodiode array (first region) on the same substrate. This spatial differentiation allows the photodiodes to occupy maximum area for high resolution while ADCs are positioned in dedicated zones, maintaining both manufacturing simplicity and sensor precision.
3Measurement precision
If photodiodes are exposed to X-ray radiation, then radiation detection sensitivity is improved, but photodiode performance degrades due to radiation damage
Solution Approach 1:
The patent converts the harmful effect of X-ray radiation into a beneficial detection signal by using the radiation-induced electron-hole pairs in the photodiodes as the measurement signal. The radiation damage is managed through device design that tolerates or recovers from radiation effects, allowing continuous operation in high-radiation environments.
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 design achieves high image resolution at reduced manufacturing complexity and cost, ensuring X-ray radiation tolerance and efficient signal processing while minimizing unnecessary radiation exposure.
Implementation Method 1
A multitude of photodiodes that are configured to convert received electromagnetic radiation such as visible light into an electrical signal
Implementation Method 2
The doped surface region reduces leakage charges generated by the reception of a higher-energy radiation such as an X-ray radiation
Data Source
AI summary
An image sensor includes a multitude of photodiodes and analog-to-digital converters disposed in adjacent first and second portions of a semiconductor substrate. The photodiodes exhibit X-ray radiation tolerance. An arrangement of several image sensors in adjacent rows can be used for an X-ray detector in a computed tomography apparatus.