Abstract
We present passive, visible light silicon nitride waveguides fabricated on ≈ 100 µm thick 200 mm silicon wafers using deep ultraviolet lithography. The best-case propagation losses of single-mode waveguides were ≤ 2.8 dB/cm and ≤ 1.9 dB/cm over continuous wavelength ranges of 466-550 nm and 552-648 nm, respectively. In-plane waveguide crossings and multimode interference power splitters are also demonstrated. Using this platform, we realize a proof-of-concept implantable neurophotonic probe for optogenetic stimulation of rodent brains. The probe has grating coupler emitters defined on a 4 mm long, 92 µm thick shank and operates over a wide wavelength range of 430-645 nm covering the excitation spectra of multiple opsins and fluorophores used for brain stimulation and imaging.
Highlights
As foundry-fabricated silicon nitride-on-silicon (SiN-on-Si) photonic platforms on 200 mm and 300 mm substrates for telecommunication wavelengths have rapidly matured in the past several years [1,2,3,4], the opportunity opens to consider extending the manufacturing technology of the SiN waveguides to the visible spectrum
We present low-temperature plasma enhanced chemical vapour deposition (PECVD) and high-temperature low pressure chemical vapour deposition (LPCVD) SiN waveguides with SiO2 cladding formed on 200 mm Si wafers using the Advanced Micro Foundry (AMF) foundry process and their application in implantable neuroprobes
A visible light SiN waveguide platform was demonstrated on 200 mm Si wafers that have been thinned to ≈ 100 μm
Summary
As foundry-fabricated silicon nitride-on-silicon (SiN-on-Si) photonic platforms on 200 mm and 300 mm substrates for telecommunication wavelengths have rapidly matured in the past several years [1,2,3,4], the opportunity opens to consider extending the manufacturing technology of the SiN waveguides to the visible spectrum. Single-mode visible light waveguides have been demonstrated using SiN [5,6,7] and alumina (Al2O3) [8,9] on 200 mm or 300 mm Si wafers, and using aluminum nitride (AlN) with chip-scale fabrication [10]. In [5] on 200 mm wafers, single-mode SiN waveguides formed by plasma enhanced chemical vapour deposition (PECVD) exhibited a loss of about 1 dB/cm at a wavelength of 532 nm. SiN generally exhibited higher losses than Al2O3 in that demonstration, the CMOS compatibility and fabrication maturity of SiN makes it a promising material for further development for visible light integrated photonics platforms. The waveguide losses are sufficiently low to be suitable for further demonstrations and developments of visible light photonic integrated circuits on Si substrates. As an example application, we demonstrate implantable neuroprobes for optogenetic stimulation using the PECVD SiN waveguides
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