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PhD Thesis Defense: Kaitlin Anagnost

Apr

13

Thursday
12:00pm - 2:00pm ET

Jackson Conf Rm/Online

To attend via videoconference, email kaitlin.anagnost.th@dartmouth.edu

"Extending the Wavelength Response of Photon-Counting Image Sensors"

Abstract

Non-visible imaging is used in a variety of applications, including medical imaging, security, astronomy, light detection and ranging (LiDAR), and more. Typical silicon-based detectors are primarily limited to the visible spectral regime, with weak responses to ultraviolet and infrared (IR) light. To improve the sensor's quantum efficiency for x-rays, for example, a scintillating layer may be deposited at the cost of decreased spatial resolution. State-of-the-art IR detectors, on the other hand, use HgCdTe in favor of silicon, increasing cost and decreasing long-term reliability.

Silicon-based detectors with photon conversion layers are presented in this thesis as possible approaches to extend the wavelength response into the x-ray and IR spectral regimes. A photon attenuation layer (PAL) is first described for better x-ray sensitivity to mitigate the quantum efficiency vs. spatial resolution trade-off in scintillators. Next, silicon's IR response is improved by considering GeSn and various III-V materials for deposition on CMOS image sensors. The band structures and detector parameters for these materials on silicon are calculated and compared to find the most favorable IR absorber.

The deposition process for the photon conversion layers can cause the pixel's transfer gate to lose functionality. CMOS image sensors without transfer gates, called 3-T pixels, are used to prevent this problem, but are dominated by kTC noise each time the device is reset. To combat this issue, a reset noise reduction method utilizing a feedback amplifier is correspondingly discussed, with both theoretical and experimental results presented.

A novel pixel using an IR absorbing layer for LiDAR applications is proposed next to bring the IR absorbing layer to market. Single photon avalanche diodes (SPADs) are the current state-of-the-art detectors for direct time-of-flight applications because of their high speed and superior timing resolution. Quanta Image Sensors (QIS) have smaller pixel pitch and lower power dissipation per event, however. A pixel design with the advantages of each detector is presented and the simulation results are analyzed. Associated readout circuitry using a time-gating approach is also discussed and theoretical proof-of-concept is demonstrated.

Thesis Committee

  • Prof. Fossum (chair)
  • Prof. Liu
  • Prof. Odame
  • Dr. Mike Hoenk (external)

Contact

For more information, contact Theresa Fuller at theresa.d.fuller@dartmouth.edu.