30-07-2012, 03:34 PM
A Piezoresistive Micro Pressure Sensor Fabricated by Commercial DPDM CMOS Process
[attachment=29557]
Abstract
A piezoresistive pressure sensor with a chip area of 2 mm 4 mm has been fabricated by a
standard CMOS process with additional MEMS post- process. The structure layers follow the design
rules of the CMOS 0.8 m DPDM (Double-Polysilicon-Double-Metal) multiple-project-wafer
foundry service provided by the Chip Implementation Center, Taiwan. We used a finite element
method software ANSYS to analyze the mechanical behavior of the pressure sensor and used the
commercial software CADENCE to design the structure layout. After the CMOS process and the
MEMS post- process, two CMOS pressure sensors with different diaphragm thickness were packaged
and tested. The sensitivities of sensors were measured as 0.53 mV/atm/V and 13.1 mV/atm/V with
non-linearity less than 5% (FSO), and agree with the theoretical prediction qualitatively.
Introduction
For the great progress of MEMS (Micro-Electro-
Mechanical Systems) [1] in recent years, there are at
least four kinds of processing methods including silicon
bulk micro-machining, silicon surface micro-machining,
LIGA [2] and CMOS (complementary metal-oxide-semiconductor)
process [3] to fabricate the micro-sensors at
present. Among these technologies, CMOS process for
micro-sensors has the advantages of the maturity in IC
(integrated circuit) foundry, the sub-micrometer spatial
resolution of device fabrication and the functionality of
on-chip circuitry.
Design of MEMS Post-process
CMOS planar process makes composite layered
structures of sensors only. It needs a MEMS post-process
for completing the three-dimensional structure of the
sensors. Sacrificial-layer removing or silicon etching on
the front-side of silicon substrate is usually selected to release
the levitation structures of accelerometers and thermal
(infrared) sensors [34]. But for the requirement of
air-sealing of the diaphragm structure herein, the anisotropic
wet etching from the backside of the silicon substrate
is chosen in this pressure sensor design. The followings
depict the MEMS post-process.
Conclusions
We successfully fabricated CMOS piezoresistive
pressure sensors by the commercial CMOS 0.8 m
DPDM process combined with MEMS post-process
etching step. The sensitivity of a sensor with a 20 m
thick diaphragm is 0.530 mV/atm/V with pressure range
from 0 to 3.4 atm, whereas the sensitivity of another
sensor with a 4 m thick diaphragm is 13.1 mV/atm/V
with pressure range from 0 to 0.75 atm. These results
agree with each other qualitatively by the theoretical
prediction derived from the dimensionless analysis in
this paper.
[attachment=29557]
Abstract
A piezoresistive pressure sensor with a chip area of 2 mm 4 mm has been fabricated by a
standard CMOS process with additional MEMS post- process. The structure layers follow the design
rules of the CMOS 0.8 m DPDM (Double-Polysilicon-Double-Metal) multiple-project-wafer
foundry service provided by the Chip Implementation Center, Taiwan. We used a finite element
method software ANSYS to analyze the mechanical behavior of the pressure sensor and used the
commercial software CADENCE to design the structure layout. After the CMOS process and the
MEMS post- process, two CMOS pressure sensors with different diaphragm thickness were packaged
and tested. The sensitivities of sensors were measured as 0.53 mV/atm/V and 13.1 mV/atm/V with
non-linearity less than 5% (FSO), and agree with the theoretical prediction qualitatively.
Introduction
For the great progress of MEMS (Micro-Electro-
Mechanical Systems) [1] in recent years, there are at
least four kinds of processing methods including silicon
bulk micro-machining, silicon surface micro-machining,
LIGA [2] and CMOS (complementary metal-oxide-semiconductor)
process [3] to fabricate the micro-sensors at
present. Among these technologies, CMOS process for
micro-sensors has the advantages of the maturity in IC
(integrated circuit) foundry, the sub-micrometer spatial
resolution of device fabrication and the functionality of
on-chip circuitry.
Design of MEMS Post-process
CMOS planar process makes composite layered
structures of sensors only. It needs a MEMS post-process
for completing the three-dimensional structure of the
sensors. Sacrificial-layer removing or silicon etching on
the front-side of silicon substrate is usually selected to release
the levitation structures of accelerometers and thermal
(infrared) sensors [34]. But for the requirement of
air-sealing of the diaphragm structure herein, the anisotropic
wet etching from the backside of the silicon substrate
is chosen in this pressure sensor design. The followings
depict the MEMS post-process.
Conclusions
We successfully fabricated CMOS piezoresistive
pressure sensors by the commercial CMOS 0.8 m
DPDM process combined with MEMS post-process
etching step. The sensitivity of a sensor with a 20 m
thick diaphragm is 0.530 mV/atm/V with pressure range
from 0 to 3.4 atm, whereas the sensitivity of another
sensor with a 4 m thick diaphragm is 13.1 mV/atm/V
with pressure range from 0 to 0.75 atm. These results
agree with each other qualitatively by the theoretical
prediction derived from the dimensionless analysis in
this paper.