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

Hyunjoo J. Lee hyunjoo at
Tue Mar 6 14:48:40 PST 2012

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


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




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


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.


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