Optical Sensor MEMS Bonding With Post-Formed Infrared Filter
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional methods for integrating biometric sensors in electronic devices face challenges due to high stress and thermal effects, leading to performance degradation in optical sensors, particularly in fingerprint recognition systems, where infrared cut-off filters and silicon microelectromechanical systems (MEMS) structures cause wafer bonding issues and affect the optical properties of complementary metal oxide semiconductor (CMOS) image sensors.
Innovation Solution
A novel sensing apparatus is developed, featuring a silicon MEMS structure bonded onto a passive oxide layer over a CMOS image sensor (CIS) wafer with a buried oxide layer and an infrared cut-off filter (IRCF) on top, where the IRCF is patterned and formed after bonding, and the MEMS structure is fabricated separately to mitigate stress and thermal effects, and the IRCF is formed after bonding to avoid wafer bonding challenges.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the infrared cut-off filter (IRCF) is deposited directly on the CMOS image sensor (CIS) wafer before wafer bonding, then the optical filtering function is achieved, but the high stress in the IRCF induces a high bow surface that makes wafer bonding difficult
Solution Approach 1:
The patent divides the structure into separate layers: the IRCF is deposited on the CIS wafer, then a planarization layer is deposited over the IRCF to create a smooth bonding surface. This segmentation allows the IRCF to maintain its optical filtering function while the planarization layer provides the smooth surface needed for successful wafer bonding, resolving the contradiction between optical function and bonding ease.
2Ease of manufacture
If deep silicon etching is performed to form silicon MEMS structure after IRCF deposition, then the MEMS structure is created, but the processes impact optical property function through extra thermal and stress effects
Solution Approach 1:
The patent performs the deep silicon etching to form the MEMS structure before depositing the IRCF. By completing the MEMS fabrication beforehand, the subsequent IRCF deposition and wafer bonding processes do not expose the MEMS structure to additional thermal and stress effects that would degrade its optical properties, thus resolving the contradiction between ease of manufacture and reliability of optical function.
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 enhances the signal-to-noise ratio (SNR) of incident light and reduces performance degradation, resulting in improved accuracy and reliability of biometric data detection by minimizing stress and thermal impacts on the optical sensors.
Implementation Method 1
an infrared cut-off filter (IRCF) on top... enhance the signal-to-noise ratio (SNR) of incident light
Implementation Method 2
a passive oxide layer over a CMOS image sensor (CIS) wafer with a buried oxide layer
Implementation Method 3
bonded onto a passive oxide layer... a first wafer including a MEMS structure and a second wafer including a CIS structure are formed separately. Then an alignment fusion bonding is performed to bond the first wafer onto the second wafer
Data Source
AI summary
Optical sensors and their making methods are described herein. In some embodiments, a described sensing apparatus includes: an image sensor; a collimator above the image sensor, wherein the collimator includes an array of apertures; and an optical filtering layer above the collimator, wherein the optical filtering layer is configured to filter a portion of light to be transmitted into the array of apertures.