Hindawi Publishing Corporation
Journal of Control Science and Engineering
Volume 2012, Article ID 923617, 5 pages
doi:10.1155/2012/923617
Research Article
Processing Chip for Thin Film Bulk Acoustic
Resonator Mass Sensor
Pengcheng Jin, Shurong Dong, Hao Jin, and Mengjun Wu
Department of ISEE, Zhejiang University, Hangzhou 310058, China
Correspondence should be addressed to Shurong Dong, dongshurong@zju.edu.cn
Received 12 January 2012; Revised 22 May 2012; Accepted 8 July 2012
Academic Editor: Li Zhang
Copyright © 2012 Pengcheng Jin et al. This is an open access ar ticle distributed under the Creative Commons Attribution License,
which permits unrestricted use, dist ribution, and reproduction in any medium, provided the original work is properly cited.
Aimed at portable application, a new integrated process chip for thin film bulk acoustic resonator (FBAR) mass sensor is proposed
and verified with 0.18 um CMOS processing in this paper. The longitudinal mode FBAR with back-etched structure is fabricated,
which has resonant frequency 1.878 GHz and Q factor 1200. The FBAR oscillator, based on the current-reuse structure, is designed
with Modified Butterworth Van Dyke (MBVD) model. The result shows that the FBAR oscillator operates at 1.878 GHz with a
phase noise of
−107 dBc/Hz and −135 dBc/Hz at 10 KHz and 100 KHz frequency offset, respectively. The whole process chip size
with pads is 1300 μm
× 950 μm. The FBAR and process chip are bonded together to sense tiny mass. The measurement results
show that this chip precision is 1 KHz with the FBAR frequency gap from 25 kHz to 25 MHz.
1. Introduction
In recent years, mass sensor based on FBAR technology has
a rapid development due to its high mass sensitivity and
integrated potential [1]. FBAR mass sensor is considered
as an excellent portable healthcare sensor resolution [2, 3].
Recent researches mainly focus on relative humidit y sensor
[4], glycerol detector [5], gravimetric sensing [6], ultraviolet
sensor [7], DNA and protein detection [8], microfluidic
system [9], and so on. However, by now FBAR mass sensors
are handled with network analyzer and RF probe station,
which is massive and various with testing environment. It is
not fit to portable application. There is no paper to report
FBAR sensor signal processing chip and its FBAR oscillator.
In this paper, we presented an integrated chip, which can
be connected with FBAR to process its RF sensor signal and
show mass change value directly.
2. FBAR Sensor Design
2.1. System Scheme. FBAR structure is shown in Figure 1.
It consists of an AlN thin piezoelectric film sandwiched by
two Al metal electrodes with back-etched structure and an
adsorption layer which is used to adsorb a par ticular material
for sensor. The adsorption layer should be selected according
to the different detected target materials. The resonant
frequency will change due to the change of mass of the
target material. Conversion between frequency change and
the mass loading is described by the Sauerbrey equation [10]:
Δ f
s
=−2Δm · f
2
s
A
−1
μ
−1/2
q
ρ
−1/2
q
,
(1)
in which Δ f
s
is the frequency change, f
s
is the fundamental
resonant frequency, Δm is the mass change, A is the active
area, ρ
q
is the density, and μ
q
is the shear modulus.
The sensor process system should be designed to obtain
FBAR resonant frequency changes due to tiny mass. Usually,
the system is based on dual-path structure, shown in
Figure 2, one path for sensor signal and the other for refer-
ence signal to deembed testing environment effects change,
such as pressure, temperature, and humidity, due to the two
paths that are neighbor in one chip. Because the signals of
FBAR are always weak, an oscillator network is desig ned
to active FBAR signals to obtain 3 V output to drive the
following processing circuit. The FBAR resonant frequency
is usual about 2-3 GHz. It is too high to be processed with
normal high speed counter. Mixture frequency approach
is also not fit to FBAR sensor owing it IP3 and complex