BOD-sensor (Beam-On-Diaphragm / Bridge-On-Diaphragm silicon pressure sensor) is a monolithic resonant MEMS pressure sensor structure developed in the mid-1990s.
A microbridge (beam/resonator) is monolithically clamped via support webs (carrier beams / Trägerstege) onto a thin silicon diaphragm (membrane). Applied pressure deflects the diaphragm, which induces axial stress/tension in the beam and shifts its resonance frequency. The frequency change is detected (typically optically after acoustic excitation). This yields a quasi-linear pressure-to-frequency response. Key measured performance (from the 1995 prototype):
- Fundamental resonance ≈ 82 kHz
- Sensitivity ≈ 4.5 kHz/bar in the –0.8 to +1 bar range
- High Q possible with vacuum encapsulation By simply varying diaphragm thickness on the same layout, the usable range extends to ~0.5–12 bar. Scaling the geometry smaller enables operation up to ~100 bar (sensitivity then ≈ 141 Hz/bar).
- Starting material: single-crystal silicon (preferably ⟨110⟩ orientation)
- Nd:YAG laser micromachining creates a controlled damaged crystal zone of defined depth
- Anisotropic KOH etching (typically ~30 % KOH at ~60 °C) then releases the free-standing beam above a remaining diaphragm of precise thickness
- All features (diaphragm + support webs + beam) are formed from one monolithic substrate; etch-stop planes ({111}) produce triangular or trapezoidal beam cross-sections
This process avoids separate doping/epitaxy etch stops and supports batch fabrication while retaining the excellent mechanical properties of single-crystal silicon.
German patent DE4332653C1 (“Monolithisch integriertes Halbleiterelement…”)
- Filed September 1993 / published 1994
- Inventors: Mani Alavi, Thomas Fabula, Axel Schumacher, Hans-Joachim Wagner
- Covers the monolithic BOD structure, its use as pressure/force/acceleration/tactile sensor or electromechanical transducer, and the laser + anisotropic-etch fabrication method.
Full text, drawings and the related 1995 paper are available via tfconsult.com (Dr. Thomas Fabula’s site) and the linked GitHub repositories.
- Technical paper: H.-J. Wagner et al., “Monolithic bridge-on-diaphragm structure for pressure sensor applications,” Microsystem Technologies 1, 191–195 (1995). DOI 10.1007/BF01371494
- Overview & resources: https://tfconsult.com/monolithic-bod-structure/
- Patent & drawings: https://tfconsult.com/mems-patent/ and Espacenet DE4332653C1
- GitHub archive (ANSYS models, figures, paper PDF, etc.): https://github.com/ThomasFabula/BOD-sensor
- beam-on-diaphragm silicon sensor,
- laser-fabricated & anisotropic etched pressure sensor,
- variable Membrandicken unter Druckbelastung