Light Detector Substrate Stack to Suppress Thermal Warpage
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Solution Overview
Problem
The existing light detection devices face warpage and cracking issues due to temperature changes, primarily because of the difference in thermal expansion coefficients between compound semiconductor and silicon substrates, leading to uneven contraction and expansion.
Innovation Solution
Incorporating an insulating film with a lower thermal expansion coefficient than the compound semiconductor substrate, featuring varying thickness portions to mitigate warpage, and ensuring the second thicker portion is at least 2 μm to further suppress substrate warpage effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If compound semiconductor substrate and silicon substrate are joined directly, then device functionality is achieved, but warpage and cracking occur due to thermal expansion coefficient mismatch
Solution Approach 1:
An insulating film is introduced as an intermediary layer between the compound semiconductor substrate and silicon substrate. This intermediate layer has a thermal expansion coefficient that is lower than that of the compound semiconductor, helping to balance the thermal stress and reduce warpage caused by the mismatch between the two substrates.
Solution Approach 2:
The thermal expansion coefficient parameter is modified by introducing the insulating film with a specific thermal expansion coefficient that is lower than the compound semiconductor but higher than silicon. This parameter adjustment balances the thermal stress distribution and prevents excessive warpage.
2Stability of the object's composition
If insulating film with lower thermal expansion coefficient is added, then warpage is suppressed, but device structure becomes more complex
Solution Approach 1:
The insulating film serves multiple functions: it acts as a thermal expansion buffer to suppress warpage, provides electrical insulation between the compound semiconductor substrate and silicon substrate, and serves as a structural support layer. By combining multiple functions in a single layer, the overall device complexity is minimized.
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 insulating film effectively reduces warpage and the likelihood of cracking in both the compound semiconductor and silicon substrates during temperature changes, maintaining device integrity and functionality.
Implementation Method 1
The insulating film contains an insulating material having a lower thermal expansion coefficient than a compound semiconductor contained in the compound semiconductor substrate
Data Source
AI summary
A light detection device includes a sensor array and a readout circuit. The sensor array includes a compound semiconductor substrate having a first main surface and a second main surface opposite to the first main surface, a plurality of photodetectors arranged two-dimensionally on the first main surface, and an insulating film disposed on the second main surface. The readout circuit includes a silicon substrate having a third main surface connected to the first main surface of the compound semiconductor substrate. The insulating film contains an insulating material having a lower thermal expansion coefficient than a compound semiconductor contained in the compound semiconductor substrate. The insulating film includes at least one first portion having a first thickness and a second portion having a second thickness larger than the first thickness.