Office of Technology Transfer – University of Michigan

a-Si Photodetectors for Under-Display Fingerprint Sensors and for Gesture Sensors

Technology #2019-132

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Lingjie Jay Guo
Electrical Engineering and Computer Science
Managed By
Joohee Kim
Licensing Specialist, Physical Sciences & Engineering 734-764-8202
Patent Protection

PCT Patent Application Filed

Today, over 1.4 billion people have smartphones, nearly half of which have fingerprint sensors as a convenient and fast way for users to unlock their devices. Until recently, fingerprint sensors have required a capacitive touch sensor that either occupies valuable space on the front of the phone in the form of a button, or is inconveniently located on the back of the phone. In 2018, new photodetectors that can be situated under the phone screen began replacing capacitive touch sensors, allowing for maximum screen to body ratios. However, thus far these in-display sensors have been made of crystalline silicon, adding manufacturing costs and complexity because they do not readily integrate with the traditional backplane control circuitry of phones, which are made of amorphous silicon (a-Si).

a-Si Photodetectors Enable Integrated In-Display Fingerprint and Gesture Sensors 

Using the same material as existing smartphone circuitry, a non-semiconductor-based photodetector enables seamless in-display fingerprint sensor integration. This new photodetector uses a-Si combined with metal oxide materials as electron transport layers to create a narrow conduction band that aligns with the valence band of a-Si. Testing has shown an excellent linear dynamic range of 190 dB with 1 µsec response time. This solution will significantly reduce manufacturing costs to make in-display fingerprint sensing readily accessible in the booming smartphone industry.


  • Smartphones
  • Tablets and notebooks


  • High screen to body ratio
  • Integration with control circuitry
  • Reduced manufacturing cost
  • Low-light detection