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Within the upcoming PIC platform, we have designed, fabricated, and examined various ring resonators, comprised of coupling structures, waveguides and ring resonators, tailored for the optical L-band (1565 nm – 1625 nm). The arrangement of the coupling structures for incoupling the light from a laser source and outcoupling of the light to a detector allows for automatic probing and mapping of various structure modifications. With grating couplers integrated on the chip, these optical structures can be linked to a tunable laser source and a detector via optical fibers.
We compare the fabrication results of the optical nanostructures for the AlN-based devices with previous results from Si3N4-based structures. To ensure the ideal structure dimensions and to minimize deviations from the simulated design values, the AlN dry etch process has been investigated and improved.
Fully CMOS-compatible pyroelectric infrared detector based on doped HfO2 thin film in 3D-integration
Pyroelectric detectors are widely used thermal infrared detectors due to their simple construction, robustness, and excellent performance. Most pyroelectric devices are based on monocrystalline lithium tantalate (LT) or pyroelectric lead zirconate titanate (PZT) thin films deposited on silicon (Si) substrate. In comparison, recently discovered pyroelectric doped hafnium oxide (HfO2) offers the possibility to manufacture completely CMOS-compatible devices on large silicon wafers.
Three-dimensional substrates with trench structures were applied for detectors to multiply the pyroelectric current responsivity of a thin, doped hafnium oxide layer deposited by atomic layer deposition. Micromechanical structuring of the 6” silicon wafers was used to improve the thermal conversion and effective plasmonic absorbers for the spectral range 3 - 5 μm.
An effective pyrocoefficient up to 1300 μC/m²/K was measured, depending on various dopants (Si, Al, La), layer thicknesses and polarization conditions. A high infrared light absorption > 80% of the plasmonic absorber in the relevant spectral range was determined using FTIR reflection measurements. The performance of the sensor element has been evaluated with a conventional analog transimpedance amplifier with a feedback resistance of 5 GΩ. A specific detectivity D* > 1 ∙ 107 cm√Hz/W (black body 1000 K, 3 - 5 μm) was measured for the frequency range 1 - 10 Hz.
Additionally, a new application-specific integrated circuit (ASIC) was used for the electrical signal conditioning to realize the first fully CMOS-compatible pyroelectric detector. This detector offers a flexible configuration, digital communication interface and achieves a similar signal-to-noise performance as the analog detectors.
We present a FPI with a (TiO2/SiO2)3 reflector stack with a reflectance of 97 % and TiO2 as high refractive index layer for the use in the VIS-range of 555 nm to 585 nm. Main achievements of TiO2 instead of Si3N4 are a higher reflectance and a minimized reflector complexity. Furthermore, we introduce a dry etch process which is compatible and integrated in the manufacturing process chain of the MEMS FPI.
Manufacturing of the 7.5 mm x 7.5 mm chip size FPI is done on 6" wafers consisting of a moveable reflector on a 210 nm thin and 5 mm in diameter LP-Si3N4 membrane and a fixed reflector with an aperture of 2 mm in diameter. The measured peak transmittance is between 28 % and 37 % with a FWHM bandwidth between 1.5 nm and 1.8 nm. It could be shown that the FPIs are tunable over the spectral range from 555 nm to 585 nm with a maximum control voltage of 45 V using the 18th interference order.
As an alternative to the alternating layer stack reflector, nanostructured photonic crystal (PhC) reflectors indicate equivalent performance by using only one layer leading to a minimized reflector complexity. This contribution presents a novel PhC reflector consisting of a 400 nm thin moveable nanostructured LP-CVD Si3N4 membrane realizing an aperture of 0.5 mm and 1 mm for reflectivity in the VIS range. Manufacturing of the reflectors is done on 6" wafers. The array of nanostructures is designed as 1 mm circular dies consisting of 436 nm wide holes with 545 nm pitch. The circular dies are arranged in an 8 x 8 matrix on the wafers with 7.5 mm pitch. Manufacturing and integration of the PhC reflectors into MEMS is realized by eBeam and nanoimprint lithography (NIL) nanostructure replication on 50 µm thin pre-etched Si membranes combined with further dry and wet etching processes. The fabricated PhC reflectors showed 424 nm wide holes and a pitch of 549 nm with a measured reflectivity above 90 % in the spectral range from 557 to 589 nm and a maximum reflectivity of 99 %.
Tunable Fabry-Pérot interferometer with subwavelength grating reflectors for MWIR microspectrometers
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