Research Papers

An Ultraminiature MEMS Pressure Sensor With High Sensitivity for Measurement of Intramuscular Pressure (IMP) in Patients With Neuromuscular Diseases

[+] Author and Article Information
A. S. Sezen1

Department of Mechanical and Manufacturing Engineering, St. Cloud State University, St. Cloud, MN 56301ssezen@stcloudstate.edu

R. Rajamani

Department of Mechanical Engineering, University of Minnesota-Twin Cities, 111 Church Street SE, Minneapolis, MN 55455

D. Morrow, K. R. Kaufman

Department of Orthopedics, Mayo Clinic, 200 First Street SW, Rochester, MN 55905

B. K. Gilbert

Special Purpose Processor Development Group, Mayo Clinic, 200 First Street SW, Rochester, MN 55905


Corresponding author.

J. Med. Devices 3(3), 031006 (Sep 01, 2009) (9 pages) doi:10.1115/1.3192103 History: Received February 13, 2009; Revised May 20, 2009; Published September 01, 2009

An ultraminiature micropressure sensor to accurately measure intramuscular pressure has been developed. The MEMS sensor is fabricated through surface micromachining and consists of a capacitive array of eight 150μm diameter sensing membranes connected in parallel. The membranes have been vacuum-sealed via a subsequent deposition and patterning batch microfabrication step. A deep reactive ion etcher (DRIE) based postfabrication self-release has been utilized to fabricate individual devices. Each device has an outline that incorporates specially designed “anchor” structures that are utilized to attach on the muscle tissue during measurements to minimize the effect of muscle contractions on sensor readings. Electrical isolation of the wire bonds and bonding pads has been accomplished by utilizing glob-topping technique. The fabricated sensor performance has been experimentally validated inside a pressure chamber. The current sensors have 0.2 mm Hg pressure resolution in the ±19mmHg dynamic range with negligible hysteresis and show a flat frequency response in the 0–5.5 Hz experimental test range.

Copyright © 2009 by American Society of Mechanical Engineers
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Figure 1

A MEMS capacitive transducer and the equivalent electrical circuit

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Figure 2

The fabrication scheme for the MEMS pressure sensors

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Figure 3

(a) Partially released and (b) fully released capacitive membranes without etch-hole plugs

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Figure 4

A successfully fabricated MEMS pressure sensor array

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Figure 5

The sandwiched metallization layer concept

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Figure 6

The sensor capacitance and electrical sensitivity with changing thickness of membrane material in the capacitive gap for a 3 μm thick SiNx membrane

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Figure 7

Closeup view of a successfully fabricated and sealed membrane

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Figure 8

The design with anchor springs: (a) the original mask layout, (b) anchor inside the needle with springs deflected, and (c) anchor inside the muscle

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Figure 9

A microfabricated silicon anchor device with the tethering wire attached

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Figure 10

Glob-topping procedure: (a) “damming” of the bonding pad area and (b) a completed glob-topping isolation process

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Figure 11

Successfully fabricated anchor devices and tethering beams

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Figure 12

A successful wire-bonding performed on a tethered anchor device

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Figure 13

Simulation results for membrane response under pressure

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Figure 14

The experimental setup

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Figure 15

Experimental results for a ramp input between 0 mm Hg, −15 mm Hg, and 15 mm Hg. (a) Chamber pressure and (b) capacitance readings from the MEMS pressure sensor.

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Figure 16

Experimental results for a ramp input train between 0 mm Hg and 25 mm Hg

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Figure 17

The frequency response of the sensor




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