Stacked Imaging Device Substrates via Metal Bumps
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Solution Overview
Problem
Existing imaging devices with a photodiode array and a functional element connected by metal bumps face constraints in performance, cost, and manufacturing yield due to thermal expansion differences, pixel size limitations, and low yield in the joining process, especially when using compound semiconductor substrates with silicon substrates.
Innovation Solution
An imaging device configuration where a readout circuit substrate with a silicon base and a sensor substrate with a compound semiconductor base are attached via spacers and metal bumps, allowing for optical connection between light receiving units and light emitting units, enabling efficient information transfer without direct electrical connection on a pixel basis, thus reducing pixel size constraints and improving reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a photodiode array substrate and a functional element substrate are connected by metal bumps, then electrical connection and signal processing are achieved, but thermal expansion differences cause warping and reduce manufacturing yield
Solution Approach 1:
The imaging device is divided into two separate substrates: a first substrate containing photodiodes for light detection, and a second substrate containing functional elements for signal processing. These substrates are connected via metal bumps, allowing independent optimization of each substrate's material and structure while maintaining electrical connection. This segmentation resolves the thermal expansion conflict by enabling separate substrate designs.
Solution Approach 2:
Metal bumps serve as intermediary connection elements between the first substrate and second substrate. These bumps provide both mechanical support and electrical connection, acting as a buffer that accommodates thermal expansion differences between the two substrates during manufacturing and operation, thereby maintaining connection reliability despite material differences.
2Reliability
If the first substrate and second substrate are connected by metal bumps, then electrical connection is established, but the joining process has low yield due to thermal expansion differences
Solution Approach 1:
The imaging device is divided into two separate substrates: a first substrate containing photodiodes for light detection, and a second substrate containing functional elements for signal processing. These substrates are connected via metal bumps, allowing independent optimization of each substrate's material and structure while maintaining electrical connection. This segmentation resolves the thermal expansion conflict by enabling separate substrate designs.
Solution Approach 2:
The patent employs specific joining process parameters including heating to 150-250°C and applying pressure of 0.1-10 MPa during metal bump connection. These controlled parameter changes optimize the joining process to accommodate thermal expansion differences, improving both connection reliability and manufacturing yield by preventing defects during the bonding process.
3Adaptability or versatility
If a module includes both first substrate with photodiode array and second substrate with functional element, then signal processing capability is achieved, but pixel size is constrained by the connection form
Solution Approach 1:
The imaging device is divided into two separate substrates: a first substrate containing photodiodes for light detection, and a second substrate containing functional elements for signal processing. These substrates are connected via metal bumps, allowing independent optimization of each substrate's material and structure while maintaining electrical connection. This segmentation resolves the thermal expansion conflict by enabling separate substrate designs.
Solution Approach 2:
The patent transitions from a planar integration approach to a three-dimensional stacked architecture where the first substrate and second substrate are vertically arranged and connected via metal bumps. This dimensional change allows signal processing functionality to be added in the vertical dimension rather than consuming horizontal pixel area, thereby enabling smaller pixel sizes while maintaining full signal processing capability.
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 configuration enhances the performance and reliability of imaging devices by allowing for smaller pixel sizes and improved manufacturing yield, enabling high-quality image capture in long wavelength bands above 1.0 μm while reducing the influence of thermal expansion and warping issues.
Implementation Method 1
a light emitting unit that emits light with a light amount in accordance with a light amount detected by the first light receiving unit
Implementation Method 2
a plurality of second pixels each including a second light receiving unit that detects a light emitted from the light emitting unit of the first pixel
Data Source
AI summary
An imaging device includes a first substrate in which a plurality of first pixels each including a first light receiving unit and a light emitting unit that emits light with a light amount in accordance with a light amount detected by the first light receiving unit are provided, and a second substrate that is provided facing the first substrate and in which a plurality of second pixels each including a second light receiving unit that detects a light emitted from the light emitting unit of the first pixel and a readout circuit that outputs an image signal based on information detected by the plurality of second pixels are provided.