Low temperature direct bonding of single crystal quartz substrates for high performance optical low pass filter using amorphous SiO2 intermediate layers

We proposed a HF-assisted single crystal quartz direct bonding method at low temperature using amorphous SiO2 layer for high performance optical low pass filter (OLPF) to improve heat resistance compared with conventional OLPFs using UV-curing adhesive. Amorphous SiO2 was deposited by ion beam sputtering on backside of both infrared reflection and anti-reflection coated substrates. By the etching rate evaluation, amorphous SiO2 deposition is considered to provide high active surface useful for bonding. The HF bonded sample with amorphous SiO2 layer achieved 0.8 MPa in tensile test and 3.3 MPa in shear test, and also nearly 100 % light transmittance was performed, which is as the same level as conventional UV-curing adhesive one. Therefore, the proposed single crystal quartz direct bonding with amorphous SiO2 layers is considered to be a promising technique to realize high performance OLPFs.