Anodic Bonding for Glass-to-Silicon Components

Anodic bonding is used to create strong and stable glass-to-silicon assemblies for MEMS devices, microfluidic chips, sensor packages and semiconductor-related components. This process is suitable when a part requires sealed cavities, aligned microchannels, wafer-level structures or reliable bonding between borosilicate glass and silicon substrates.

For projects involving glass-to-silicon bonding, the key details to confirm are material grade, glass thickness, silicon type, bonding area, channel or cavity design, alignment tolerance and working environment.

Typical parts we support include:

MEMS substrates — sealed cavities, sensor structures and wafer-level bonded parts.
Microfluidic devices — glass-silicon chips with channels, ports and reaction chambers.
Sensor packages — transparent glass covers bonded to silicon-based structures.
Semiconductor components — process-related glass-silicon assemblies requiring stable bonding and clean interfaces.

We can review custom anodic bonding requirements according to drawings, material combination, surface condition, bonding area, alignment accuracy, quantity and final application.

What Is Optical Contact Bonding?

Optical contact bonding is an adhesive-free joining technique in which two precision-polished optical surfaces are brought into intimate contact and held together by van der Waals molecular forces — without any cement, adhesive, or applied heat. When both surfaces are sufficiently flat (typically λ/10 or better) and free of contamination, the intermolecular attraction across the interface is strong enough to create a permanent or semi-permanent bond. The resulting joint is optically transparent, introduces no additional refractive index discontinuity beyond the glass itself, and exhibits exceptional dimensional stability. Optical contact bonding is widely used in the fabrication of etalons, beam splitters, prism assemblies, and laser cavity components where adhesive-induced wavefront distortion or outgassing cannot be tolerated.

Process Capabilities

Surface Flatness Requirement: λ/10 or better (per bonding surface)
Surface Roughness (Ra): ≤ 0.5 nm (superpolished finish)
Bond Strength: ≥ 1 MPa (van der Waals contact); up to 10+ MPa (hydroxide-catalysis bonding)
Transmitted Wavefront Error: λ/10 – λ/20 across aperture
Parallelism of Bonded Assembly: ≤ 2 arcsec
Maximum Substrate Size: Up to 200 mm diameter
Operating Temperature Range: –40 °C to +300 °C (material-dependent)

Compatible Materials

1	Fused Silica	Corning 7980 / Tosoh ES-2000
2	Quartz Glass	SCHOTT Lithosil Q / Heraeus Suprasil 1
3	Borosilicate Glass	PYREX 7740 / BOROFLOAT 33
4	Sapphire	C-plane / A-plane
5	Silicon	Float Zone / Czochralski
6	Glass-Ceramic	ZERODUR / PYROCERAM 9606
7	Optical Glass	BK7 / N-BK7
8	CaF₂	UV-grade / IR-grade
9	MgF₂	UV-grade
10	ZnSe	CVD-grade
11	Germanium	Single crystal / Polycrystalline

Surface Finish Standards

Flatness: λ/10 per surface (λ/4 minimum for contact bonding)
Surface Roughness: Ra ≤ 0.5 nm (superpolish required for reliable bond)
Scratch-Dig: 10-5 (laser-grade, per MIL-PRF-13830)
Cleanliness: ISO Class 5 cleanroom bonding environment
Bond Interface Inspection: Newton's rings / interferometric fringe inspection before and after bonding
Post-Bond Flatness: Assembly TWE ≤ λ/10 guaranteed

Typical Applications

Fabry-Pérot Etalons: Ultra-stable spacer assemblies with no adhesive layer
Laser Optics: Intra-cavity windows, output couplers, and polarizers for high-power lasers
Interferometry Components: Reference flats and beam splitter cubes for metrology instruments
Gravitational Wave Detectors: Hydroxide-catalysis bonded mirror suspensions (LIGO-type)
Space Optics: Adhesive-free assemblies for vacuum and radiation environments
Optical Isolators & Retarders: Cemented-free crystal and glass assemblies

Custom Specifications

We support both standard van der Waals contact bonding and hydroxide-catalysis (silicate) bonding for applications requiring higher bond strength or elevated temperature stability. Custom assemblies can include dissimilar material pairs (e.g., fused silica to sapphire), multi-element stacks, and bonded assemblies with applied AR or HR coatings on external surfaces. All bonding is performed in a controlled cleanroom environment with full interferometric inspection at each stage. Documentation includes surface figure maps, fringe pattern records, and dimensional reports for every bonded assembly.