EE Ph.D. Oral Examination: Hyunjoo Jenny Lee, March 7, at 2:00 pm, Nano 232

Stanford University Ph.D. Oral Examination – Department of Electrical Engineering

 

Title: Capacitive Micromachined Ultrasonic Transducer (CMUT) Chemical Sensor And Its Interface Circuits

Speaker:  Hyunjoo Jenny Lee

Advisor:  Professor Pierre Khuri-Yakub

Date:  March 7, 2012 (Wednesday)

Time:  2:00 pm (refreshments at 1:45 pm)

Location: Nanoscale Science and Engineering (Nano) - Room 232

 

Abstract:

 

Miniaturized chemical sensors based on microelectromechanical-systems (MEMS) offer competitive advantages over the existing bench-top chemical analyzers, such as small size, low power consumption, low cost due to batch fabrication, and CMOS compatibility. The potential for system integration of these chemical sensors with on-chip CMOS circuitry expands the spectrum of use, including consumer, industrial, and homeland security applications.

 

In the first part of this talk, I will introduce a miniaturized resonant chemical sensor based on a 50-MHz capacitive micromachined ultrasonic transducer (CMUT). With a high mass sensitivity of 3.3 ag/Hz, this CMUT-based chemical sensor achieves excellent volume sensitivity of 21 pptv/Hz to dimethyl methylphosphonate (DMMP), a common simulant for sarin gas.

 

In the second part, I will introduce a direct application of the mesoporous silica thin-film on a CMUT for relative humidity and CO₂ detection. Using mesoporous silica thin-film with a pore size of  ~11 nm, this sensor achieves one of the lowest volume resolutions and a sensitive detection of 5.1 × 10^-4%RH/Hz to water vapor in N₂. In addition, a mesoporous thin-film that is functionalized with an amino-group is directly applied on the resonant sensor, which exhibits a volume sensitivity of 1.6 × 10^-4%/Hz and a volume resolution of 1.82 × 10^-4% to CO₂ in N₂.

 

In the last part of my talk, I will focus on the sensor interface circuitry for CMUT and discuss the frequency noise analysis of CMUT-based oscillators. Specifically, I will introduce a multi-channel interface integrated circuit (IC) implemented using 0.18-um CMOS technology, which results in reduced area and power consumption for each channel. Two-channel detection of relative humidity is demonstrated using this circuit.