Capacitive micromachined ultrasonic transducer (CMUT) for chemical detection in air
Abstract/Contents
- Abstract
- Demand for a highly sensitive, accurate, and portable chemical sensor system has been increasing over the recent years for a wide range of applications. For these applications; resonant chemical sensors based on the mass-loading effect (i.e., gravimetric sensors) with chemical functionalization layers are promising candidates. Among them, a capacitive micromachined ultrasonic transducer (CMUT) is a strong candidate with key advantages: 1) it utilizes a thin resonator backed by a vacuum cavity which results in a high quality factor, 2) it has the ability to apply massive parallelism, thereby, increasing its reliability and lowering the motional impedance, and 3) consistent repeatability and reliability in the fabrication process. The development of a CMUT-based chemical sensor encompasses device selection and characterization, oscillation circuit design and implementation, chemical functionalization, and a chemical test. CMUTs with a resonant frequency ranging from 6 MHz to 50 MHz are selected. An oscillation circuit is designed to track the parallel resonant frequency of the CMUT. The CMUT is chemically activated by thin polymer layers (e.g., Polyisobutylene or synthesized polymer) to absorb an analyte of interest. Chemical experimentation reveals that the CMUT-based chemical sensor has a high sensitivity, the capability of analyte identification, and a reliable operation. In order to improve the performance of the CMUT as a mass-loading sensor, the device should have the following elements: a thin plate with a high frequency, low parasitic capacitance, low operating voltage, and a high breakdown voltage. The local oxidation of silicon/wafer-bonding (LOCOS/wafer-bonding) process meets this criteria. The process realizes a CMUT with a quality factor of 400 in air, a resonant frequency up to 50 MHz, and an unprecedented small gap of 40-nm. This thesis presents a highly sensitive chemical sensor based on the CMUT technology with theoretical mass sensitivities of 54.4 zg/Hz/um^2 for the devices operating at 50 MHz. The multi-resonator configuration is more reliable in operation and makes the oscillator circuit easier to design. Since the oscillator circuit was designed with low-frequency (0.2 Hz) noise and an equivalent volume resolution of 21 ppt of Dimethyl methylphosphonate (DMMP); a simulant of Sarin (GB) was achieved. This work thus demonstrates that CMUT technology has great potential for the implementation of chemical sensing systems that are sensitive; yet reliable and portable.
Description
| Type of resource | text |
|---|---|
| Form | electronic; electronic resource; remote |
| Extent | 1 online resource. |
| Publication date | 2011 |
| Issuance | monographic |
| Language | English |
Creators/Contributors
| Associated with | Park, Kwan Kyu |
|---|---|
| Associated with | Stanford University, Department of Mechanical Engineering |
| Primary advisor | Kenny, Thomas William |
| Primary advisor | Khuri-Yakub, Butrus T, 1948- |
| Thesis advisor | Kenny, Thomas William |
| Thesis advisor | Khuri-Yakub, Butrus T, 1948- |
| Thesis advisor | Howe, Roger Thomas |
| Advisor | Howe, Roger Thomas |
Subjects
| Genre | Theses |
|---|
Bibliographic information
| Statement of responsibility | Kwan Kyu Park. |
|---|---|
| Note | Submitted to the Department of Mechanical Engineering. |
| Thesis | Thesis (Ph.D.)--Stanford University, 2011. |
| Location | electronic resource |
Access conditions
- Copyright
- © 2011 by Kwan Kyu Park
- License
- This work is licensed under a Creative Commons Attribution Non Commercial 3.0 Unported license (CC BY-NC).
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