A real, commercially shipped accelerometer from
Analog Devices.
🔬
A comb-like plate suspended from folded springs
forms the inertial mass. Stationary polysilicon
finger electrodes interleave with fingers on the
moving mass, and the displacement between them is
measured capacitively.
The die measures 1.94 mm × 1.94 mm, with an
8-signal-port sensor region of 753 µm × 657 µm.
INSIDE THE SENSOR CELL
Anchors, mass, and fingers
AnchorFixes the spring structure to the substrate
Proof massThe suspended comb structure that moves
Position sense region42 cells, measuring displacement
Self-test region12 cells, electrostatically shake the mass to test it
The related ADXL-50 uses 3 sets of 2 µm-thick
polysilicon fingers — 2 fixed, and 1 movable set
suspended just 1 µm above the base.
SPEC SHEET
ADXL150 design specifications
Resonant frequency24 kHz
Bandwidth400 to 1000 Hz
Sensitivity38 mV/g
Full-scale range±50g
Supply voltage4–6 V
Notice the resonant frequency (24 kHz) sits well
above the bandwidth (up to 1000 Hz) — exactly the
design rule from earlier.
Capacitance≈ 100 fF across 42 parallel sensor cells
Spring constantk ≈ 5.6 N/m from beam geometry (ADI measured 5.4 N/m)
Resonant frequency≈ 24.7 kHz, from k and the proof mass
Quality factor≈ 120, from air damping under the proof mass (Couette flow)
Hand calculations from beam bending and gas
damping land within a couple percent of ADI's own
measured numbers — the physics really does predict
the chip.
BACK TO FABRICATION
Built with what you already know
Once the mechanical design is set, the ADXL150 is
built with the same tools you learned in earlier
units: deposition, patterning, CVD oxide and
nitride, and a final metallization step — then
released, just like a PolyMUMPs device.
⚙️ → 📈
Accelerometer design isn't a separate skill from
fabrication — it's the same fabrication knowledge,
aimed at a specific mechanical goal.