Wheatstone Bridge
MEMS Pressure Sensor

Design, Fabrication, and Testing of a MEMS-Based Pressure Sensor

Wheatstone Bridge Configuration
Figure 1: Pressure Sensor with Wheatstone Bridge Configuration
Cross-sectional view
Figure 2: Cross-sectional view of the sensor

Project Overview

This project was developed under the course EGN5013C: Introduction to Nanofabrication at Florida International University. The goal was to design, fabricate, and test a MEMS-based pressure sensor leveraging standard cleanroom-based microfabrication techniques. The Wheatstone bridge configuration allows precise measurement of small pressure-induced resistance changes.

Design & Layout

The Wheatstone bridge sensor consists of four resistive elements arranged in a bridge configuration to measure small changes in pressure. The layout was developed using LayoutEditor, with frontside and backside masks designed for layered processing.

Frontside Mask
Figure 3: Frontside Mask Design
Backside Mask
Figure 4: Backside Mask Design

Fabrication Process

Fabrication took place in a Class 100 cleanroom environment. The major process steps included:

  • Cleanroom Preparation: Class 100 cleanroom protocol adherence
  • Substrate Preparation: Spin coating using spin coater
  • Lithography: Mask alignment using OAI Mask Aligner, Laser Lithography for mask writing
  • Etching: Reactive Ion Etching (RIE) and Deep Reactive Ion Etching (MARCH DRIE)
  • Thin Film Deposition: Sputtering, Evaporation (PVD), Plasma-Enhanced CVD (PECVD)
  • Profilometry: Film thickness measurement using ALPHA STEP Profilometer
  • Packaging: Bonding with wedge bonder
Class 100 Cleanroom
Figure 5: Class 100 Cleanroom
OAI Mask Aligner
Figure 6: OAI Mask Aligner
Wafer after etching
Figure 7: Wafer after bulk silicon etching
Wheatstone bridge with membrane
Figure 8: Wheatstone bridge with membrane

Tools & Equipment Used

  • LayoutEditor
  • Heidelberg 101 Laser Lithography
  • OAI Mask Aligner
  • Reactive Ion Etching (RIE)
  • MARCH Deep RIE (DRIE)
  • PVD Sputtering System
  • PVD Evaporation System
  • Plasma-Enhanced CVD (PECVD)
  • ALPHA STEP Profilometer
  • Wedge Bonder

Testing & Results

Following fabrication, the Wheatstone bridge sensor was tested under varying pressure to validate its sensitivity and functional response. The change in resistance of the bridge arms was recorded and output voltage changes were measured to assess sensor performance.

Testing Setup
Figure 9: Pressure Sensor Testing Setup

Downloads

Conclusion

The successful fabrication and testing of a Wheatstone Bridge Pressure Sensor provided deep insights into semiconductor fabrication, thin film deposition, lithography, and cleanroom protocols. This hands-on project not only reinforced microfabrication concepts but also strengthened troubleshooting and testing skills essential in the semiconductor and MEMS industries.

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