Fixed Electrodes: Capacitance Range 10 fF to 10 pF

Component Specifications

Definition

Fixed electrodes are precision-engineered stationary conductive plates or surfaces within capacitive accelerometers that form part of a differential capacitor arrangement. They maintain a fixed position relative to the accelerometer housing while interacting with movable proof masses or seismic masses. When acceleration occurs, the movable mass deflects, changing the distance between it and the fixed electrodes, thereby altering capacitance. This capacitance change is measured and converted into an electrical signal proportional to acceleration. Fixed electrodes are critical for maintaining measurement stability, linearity, and sensitivity in MEMS (Micro-Electro-Mechanical Systems) and capacitive accelerometers used across various precision measurement applications.

Working Principle

Fixed electrodes operate on the principle of variable capacitance sensing. They form one plate of a parallel-plate capacitor system, with the movable proof mass acting as the other plate. Under acceleration, the proof mass moves relative to the fixed electrodes, changing the gap distance between them. This alters the capacitance according to C = εA/d, where ε is permittivity, A is overlapping area, and d is gap distance. The capacitance change is detected by integrated circuitry (often using AC excitation or charge amplification), converted to a voltage signal, and processed to determine acceleration magnitude and direction. Differential configurations with multiple fixed electrodes cancel common-mode noise and improve sensitivity.

Materials

Typically made from doped silicon (for MEMS devices), gold-plated beryllium copper, nickel alloys, or platinum-group metals. Silicon electrodes are often doped with phosphorus or boron to enhance conductivity. Substrates may include glass (Pyrex) or silicon with silicon dioxide insulation. Coatings may include gold for corrosion resistance or anti-stiction layers like self-assembled monolayers (SAMs).

Technical Parameters

Parameter	Typical range	Notes & selection driver
Resistance	<1 Ω (for conductive electrodes)
Gap Distance	1-10 μm (MEMS), 10-100 μm (macro)
Electrode Area	0.01-1 mm²
Capacitance Range	10 fF to 10 pF
Flatness Tolerance	<0.1 μm
Frequency Response	DC to 5 kHz
Dielectric Strength	>100 V/μm
Operating Temperature	-40°C to +125°C

Ranges are indicative industry figures for RFQ preparation, not a supplier commitment. Confirm every value and standard with the legal manufacturer before ordering.

Standards

ISO 16063-21, IEC 60747-14-1, DIN 43751

Parent Products

This component is used in the following industrial products

Accelerometer

An accelerometer is a motion sensor component that detects and measures acceleration forces, including static gravity and dynamic motion-induced forces.

View Product Details

Triaxial Accelerometer

A sensor that measures acceleration along three orthogonal axes (X, Y, Z) simultaneously.

View Product Details

Engineering Analysis

Risks & Mitigation

Electrode stiction (adhesion to proof mass)
Dielectric breakdown under high voltage
Corrosion or contamination affecting capacitance
Mechanical fatigue from vibration
Thermal expansion mismatch causing drift

FMEA Triads

Trigger: Particulate contamination between electrodes
Failure: Short circuit or capacitance drift
Mitigation: Cleanroom assembly, hermetic sealing, particle getters

Trigger: Electrostatic discharge (ESD) during handling
Failure: Dielectric breakdown or electrode damage
Mitigation: ESD-protected packaging, on-chip protection diodes, proper grounding

Trigger: Thermal cycling stress
Failure: Electrode delamination or contact failure
Mitigation: CTE-matched materials, stress-relief designs, thermal testing

Industrial Ecosystem

Compatible With

Typical Suppliers & Equivalents

Compliance & Inspection

Tolerance

Gap distance tolerance typically ±0.05 μm, electrode alignment ±0.1°, capacitance matching ±1% for differential pairs

Test Method

Capacitance measurement with LCR meters, laser interferometry for gap verification, SEM inspection for dimensional accuracy, temperature cycling per MIL-STD-883

Procurement Evaluation Criteria

A practical evidence checklist for RFQ preparation and supplier evaluation.

Technical documentation

Request current drawings, revision history, and a signed specification sheet.

Manufacturing capability

Verify equipment lists, process limits, capacity, and representative production evidence.

Inspection readiness

Confirm test methods, calibrated equipment, sampling plans, and traceable reports.

Supplier transparency

Check the legal entity, factory address, ownership, certifications, and direct contacts.

CNFX does not score or rank suppliers. Buyers must verify all claims and documents with the legal manufacturer before ordering.

Manufacturers of Fixed Electrodes

Manufacturer profiles associated with Fixed Electrodes.

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Compiled and source-reviewed by the CNFX editorial team. Each manufacturer above links to the page on that company's own website where the product is listed, with the date we checked it. How we source and review

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Frequently Asked Questions

What is the difference between fixed electrodes and movable electrodes in accelerometers?

Fixed electrodes remain stationary relative to the accelerometer housing, while movable electrodes (proof masses) deflect under acceleration. The changing distance between them creates measurable capacitance variation.

Why are multiple fixed electrodes used in some accelerometer designs?

Multiple fixed electrodes enable differential capacitance measurement, which improves sensitivity, reduces temperature drift, cancels common-mode noise, and allows measurement of acceleration in multiple axes.

How do manufacturing tolerances affect fixed electrode performance?

Tolerances in gap distance, surface flatness, and alignment directly impact capacitance baseline, sensitivity, linearity, and cross-axis sensitivity. Tight tolerances (typically <0.1 μm) are required for high-precision applications.

Data Basis

Editorial classification, named public sources where available, and source-reviewed manufacturer records. See the editorial policy.

Preliminary Technical Classification

This page supports structured research, RFQ preparation, and supplier evaluation. It does not replace buyer-led supplier qualification, standards review, or technical approval.

Fixed Electrodes