Integrated SiC Photodiode Arrays for UV-Spectroscopic Applications

We are developing unique Silicon Carbide (SiC) solar blind UV detectors with broad potential impacts in Planetary and Earth Sciences and Heliophysics. We propose to fabricate unique, passive and active, SiC UV linear sensor arrays. We will ultimately scale up our technology to fabricate 128x2 SiC active arrays with 40um pixel pitch, with a 3T amplifier readout circuit integrated directly into each pixel on-chip. In Phase 1, we designed and built prototype UV optical sensor array chips to demonstrate the proof-of-concept at TRLs 3 and 4. In Phase 2, we will enhance these to TRLs 5 and 6. Building upon Phase 1, we will fabricate a variety of arrays, including 128x2 arrays with a higher-fill-factor, 256x2 arrays for higher spectral resolution, and 32x2 and 64x2 active arrays with different readout integration. Deep trenches surrounding each pixel will provide electrical isolation to eliminate crosstalk between array elements. Readout circuits will use external signals to reset the sensors, buffer the output signal, and perform read-out selection by multiplexing. This work enjoins the unique advantages of SiC, such as its extremely low dark current, even at high temperatures, its inherent visible-blindness, and its capability to grow a native oxide, to the advantages of active pixel sensor technology, such as higher sensitivity and low power consumption, to revolutionize UV sensing in the 120 to 350 nm range. As a transformative technology, it can lead to advanced, flexible instrumentation with lower design complexity for UV spectroscopy, remote sensing, remote and in-situ characterization and imaging. By comparing SiC array characteristics with literature, and testing operational characteristics on validation systems we design, we will make first-order estimates for the arrays use in applications like remote-sensing, and Raman and reflectance spectroscopy. We will thus identify the target next-gen specifications for applications in specific instruments and missions.   We propose to build upon and scale up our Phase 1 proof of concept SiC UV sensor array prototypes to develop 128x2 pixel SiC active UV sensor arrays with pitch smaller than 40 um. An amplifier readout circuit will be integrated into each pixel. This circuit will be designed to reset the photodiodes externally, to buffer the output signal, and to allow diodes to be selected for reading out by multiplexing. To our knowledge, our technology with SiC photodiodes integrated monolithically with their active output circuits is unique. We will also build 256x2 passive arrays on the same chip to achieve even higher spectral resolution. The proposed work is to scale this prototype technology to a level where it can be used in UV-measurement instrumentation. This allows for the design of sensitive, much more complex sensor instruments benefiting from the unique advantages of SiC (high temperature operation capability, low dark current, intrinsic native oxide, visible-blindness), potentially revolutionizing UV spectroscopy and imaging for a broad set of scientific and industrial applications.     OVERALL OBJECTIVE in Phase 2 is to improve sensitivity, resolution, yield of SiC UV sensor arrays for spectroscopy in 120-350nm, and to reach TRL 6. The technical objectives are: *Demonstrate high sensitivity in the 120-350nm region by characterizing the Phase 1 arrays and adjusting our design and processes to improve optical performance, sensitivity, responsivity and crosstalk. *Design and Fabricate SiC 128x2 Linear Photodiode UV Sensor Arrays with integrated active amplifier 3T readout circuits, a 256x2 passive array to double spectral resolution, pixel arrays with wide pixels, readout circuits that were optimized in Phase 1, pixels with the readout transistors contained in each pixel. *Demonstrate pathways to an instrument-ready UV sensor chip, to a full 2D active pixel array and a full 2D passive array for imaging. *Define Science Applications and perform lab validation. DELIVERABLES are: Individual Sensors Demonstrating Spectral Sensitivity Covering the Range 120-350 nm; Fabricated: 3T amplifier readout circuit from transistors designed in Phase 1; 3T amplifier readout circuit integrated with photodiode into single pixel; 128x2 SiC Passive arrays with/without deep trench isolation, with wider pixels, A 64x2 Active Array on a single SiC chip; 256x2 Passive Arrays with/without isolation; Report detailing a path forward for the implementation of SiC arrays in instruments. 

  Visible-blind SiC UV sensors for in-situ/remote spectroscopy/imaging in Planetary and Earth Science, Heliophysics. For instance: Water signature detection, surface/atmosphere/plume characterization, mineralogy (e.g. UOP, MLE, Enceladus missions); LDEP and New Frontiers missions, LUVOIR Concept Study, CubeSat/SmallSat missions; future instruments like CUVIS (the DAVINCI+ probe); instrumentation development (PICASSO, MATISSE, DALI). Handheld units based on SiC sensors (no cooling/visible filter needed) can be of use in Artemis. Applications for UV sensing, spectroscopy and imaging include: sanitation (e.g. water/air filtration monitoring), fire and rocket plume detection, bio-detection, instrumentation, industrial monitoring, high-resolution fault inspection, and oil/gas logging systems. The high-temperature capability and inherent visible blindness of SiC allow applications in extreme conditions and simpler designs.

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