Infrared Imaging Device Indium Bump Bonding Alignment
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Solution Overview
Problem
Infrared imaging devices face challenges due to material differences between sensor and readout circuit substrates, leading to stress and reduced sensitivity from misalignment and inadequate bump spacing during flip chip bonding.
Innovation Solution
The imaging device employs a configuration with multiple absorption layers and electrodes, where upper absorption layers generate individual pixel signals and a lower absorption layer generates a common signal, using flexible metal bumps to optimize bump spacing and reduce misalignment issues.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If flip chip bonding is performed with solder bumps and heating, then strong bonding is achieved, but stress is applied to substrates due to material and thermal expansion differences
Solution Approach 1:
The patent changes the bonding parameters by using indium bumps instead of solder bumps, bonding at room temperature instead of high temperature, and applying pressure during bonding. This resolves the contradiction by achieving sufficient bonding strength without the thermal stress that would damage the substrates.
Solution Approach 2:
The patent applies different materials and bonding conditions to different parts of the assembly. Indium bumps are used specifically for their flexibility and low melting point, allowing localized adaptation to the substrate materials' thermal expansion characteristics, thereby reducing overall stress while maintaining bonding strength.
2Stress or pressure
If indium bumps are used for bonding, then substrate stress is reduced, but misalignment occurs between substrates
Solution Approach 1:
The patent incorporates alignment marks on the substrates and performs alignment operations before bonding. This preliminary action ensures precise positioning of the sensor substrate relative to the readout circuit substrate, compensating for the lack of self-alignment that would result from using flexible indium bumps.
3Manufacturing precision
If bump intervals are extended to reduce misalignment, then alignment tolerance improves, but device area increases
Solution Approach 1:
By performing alignment operations beforehand using alignment marks, the patent achieves precise substrate positioning without needing excessive spacing between bumps. This allows compact bump spacing while maintaining alignment accuracy, resolving the contradiction between alignment tolerance and device area.
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 sensitivity by allowing simultaneous detection of pixel signals without time division, while extending bump intervals to minimize misalignment and stress, thereby improving image resolution and reducing the number of common bumps.
Implementation Method 1
a plurality of first absorption layers 11 that absorb an infrared ray with a given wavelength range, and generate pixel signals of a plurality of pixels, respectively; at least one second absorption layer 12 that absorbs an infrared ray with a wavelength range which is different from the given wavelength range of the first absorption layers 11, and generates a pixel signal common to the pixels
Data Source
AI summary
An imaging device includes: a plurality of first absorption layers that absorb an infrared ray with a given wavelength range, and generate pixel signals of a plurality of pixels, respectively; at least one second absorption layer that absorbs an infrared ray with a wavelength range which is different from the given wavelength range of the first absorption layers, and generates a pixel signal common to the pixels; a plurality of first electrodes that take out the pixel signals from the first absorption layers, respectively; and a second electrode that takes out the pixel signal from the at least one second absorption layer.