A highly emissive Si-based microhotplate based on self-organizing nanostructures is presented. The silicon was structured by a self-masking deep reactive ion etching process resulting in needle-like non-periodical microstructures. Evaporated platinum settles in a kind of glancing angle deposition as well-defined nanocrystals on the silicon microstructures. Finite-difference time-domain simulation allowed the evaluation of the ideal platinum thickness for maximized infrared absorption and emission. We measured the hemispherical spectral transmittance and reflectivity of the fabricated surfaces and found the hemispherical spectral absorbance to be up to 0.97 in the investigated wavelength range. To demonstrate the advantages of these micro-nano-structures, we present the fabrication and characterization of a thermal infrared hotplate-emitter. With integrated Pt-on-Si-needles, the emitter shows a 2.6 times higher IR emission without wavelength-dependent interference patterns as compared to an uncoated Si-based emitter at the same membrane temperature.
The rear side of a pressure sensor diaphragm is prepared with an additional diamond layer as protective coating against harsh media. The preparation sequence for the diamond coating is developed as a simple backend process, combining only two additional steps in the standard process. These are the local seeding of nanodiamond layer and the low‐temperature diamond growth at <300 °C in a linear antenna microwave plasma‐enhanced chemical vapor deposition reactor, where only at the nanodiamond seeded sites, a high‐quality diamond film was synthesized. The seeding resolution in the setup used was limited to ≈80 μm, but can be further reduced. In an industry‐typical assembly sequence the diamond coated pressure sensor devices are further equipped with a support wafer and mounted to a TO‐8 socket. Tests of such sensor systems indicate that the diamond layer does not hamper the stability of the device. This proofed method of postprocessing an only‐local and low‐temperature synthesis of a diamond layer on the wafer‐level opens‐ up possibilities for many other applications, since this approach is scalable and in general cost effective.
AlGaN-based far ultraviolet-C (UVC) light emitting diodes (LEDs) with a peak emission wavelength below 240 nm typically show a long-wavelength tail at >240 nm that is detrimental to the use of the devices for skin-friendly antisepsis. We present the development of far-UVC LEDs with reduced long-wavelength emission using a HfO2/SiO2-based distributed Bragg reflector (DBR) filter. When the DBR filter is directly mounted on an LED package, the long-wavelength emission around 250 nm is reduced by two orders of magnitude while the transmitted output power is reduced down to 18%–27% of the initial value for DBR filters with cut-off wavelengths at 237–243 nm. As the transmission through the DBR filter depends strongly on the angle of incidence of the radiation, the transmitted output power of the spectrally pure far-UVC radiation can be doubled when an additional collimating lens is used on top of the LED package before passing through the filter.
For the fabrication of a micro fluidic high pressure oil sensor (400 bar) based on an infrared transmission measuring principle the bonding of 2 mm silicon wafers is necessary. Conventional bonding techniques such as silicon fusion bonding or anodic bonding are not suitable for bonding thick and inflexible silicon wafers, because these techniques can not compensate for the wafer bow. We present a new bonding procedure for silicon substrates thicker than 1 mm using a silicon adapted LTCC tape as an intermediate leveling layer. The wafers are preprocessed by etching a nano structured silicon surface on the internal side. The silicon wafers are aligned and stacked with pre-structured green LTCC tapes by an optical stacking unit. During the hot isostatic lamination at 55 bar the structured LTCC tape is adjusted to the silicon. A subsequent pressure assisted sintering leads to a wafer bonding strength up to 5000 N/cm2. With the bonding technique it is possible to create cavities and channels between the thick wafers by the use of punched and laser cut LTCC. The fabrication steps of the sandwich build-up especially the sequential lamination and the optical adjusting procedure of the flexible (LTCC) and inflexible (2 mm Wafer) substrates will be explained in detail. A method to reduce the shrinkage and distortion of the green LTCC during handling is demonstrated. The distribution of the bonding and bursting strength of the single fluidic systems on a complete sandwich substrate is analyzed.
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