Single molecule detection of volatile chemical compounds using integrated miniature avalanche gas ionization detector

About This Grant

Abstract Title: Ultrasensitive sensors for detecting gases at the single molecule level Gas sensing has a broad range of applications in environmental protection/monitoring, healthcare (such as breath analysis and body odor analysis), homeland security (explosive detection), agriculture, and industries (food, winery, and petroleum). Current gas sensors are limited by size, weight, sensitivity, and power consumption. The project aims to develop a miniature gas sensor that can detect gases at the single-molecule level. To achieve this, a semiconductor structure will be engineered to capture ions generated by ionizing gas molecules and then amplify them into an enhanced signal approximately one million-fold. Such a device will enable field-deployable gas sensing applications with a sensitivity similar to or even better than that of benchtop gas sensing instruments. The project is highly interdisciplinary, involving electrical engineering, micro/nanofabrication, semiconductor physics, material sciences, analytical chemistry, and gas analysis. It will provide vast opportunities for the participating students to learn how to synergize the knowledge and skills to advance sciences and technologies. The project will include a prominent outreach and education program, promoting awareness of and interest in engineering, physics, and bio/chemical sensing among K-12 and undergraduate students. The goal of the project is to (1) develop a miniature avalanche gas ionization detector (AGID) capable of detecting single negative/positive ions in an ambient environment (1 atm. and room temperature) with a low voltage (<50 V) and (2) integrate the AGID with micro-gas chromatography (micro-GC) for rapid and field-deployable gas analysis with unprecedented size, weight, and sensitivity. Gas sensing has a broad range of applications. Many widely used gas analysis instruments, such as gas chromatography (GC), mass spectrometry (MS), and ion mobility spectrometry (IMS), rely on “universal” gas detectors that respond to a wide range of gases after they are separated by those instruments. However, existing “universal” gas detectors either lack sufficient sensitivity or require high voltage and vacuum operation. The proposed AGID uses avalanche processes in a semiconductor P/N junction to detect positive/negative ions and electrons produced by ionizing gas molecules to achieve an ultrahigh sensitivity. The AGID can be operated in linear amplification mode (also known as analog mode) with an internal gain of >100 and Geiger mode (or counting mode) with an internal gain of ~106. The project will accomplish three aims. (1) Design/fabricate AGID to detect electrons (or negative ions) using Silicon-based CMOS technology. The AGID will be characterized and operated in both analog and Geiger mode. (2) Design/fabricate AGID to detect positive ions using Silicon- or Germanium-based CMOS technology in which holes (instead of electrons) will be used in avalanche processes. The AGID will be characterized and operated in both analog and Geiger mode. (3) Construct and benchmark an automated, fully functional, battery-powered micro-GC-AGID. The AGID enables ultrahigh sensitivity to detect single ions/electrons generated from gas molecules, while achieving a small size and low voltage/power operation at ambient pressure. A novel vertical-collection-lateral-multiplication AGID structure will be explored to leverage mature Si and Ge materials and CMOS technology, which will result in a low avalanche breakdown voltage, low fabrication cost, compact form factor, and significantly improved device reliability, scalability, and manufacturability. More importantly, Ge-based design targets positive ion detection, which has rarely been studied. The AGID can be used broadly in analytical instruments to help increase their sensitivity, reduce size/weight/power consumption, and improve operational conditions. The micro-GC-AGID synergizes AGID and micro-GC technologies to achieve an unprecedented size, weight, and sensitivity. It will be battery-powered and can be field-deployed for rapid and in situ gas analysis. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.