Andreas Krauss

Comparative study of large area pulsed laser deposited metal oxides for gas sensors applications

Large area pulsed laser deposition was used to deposit different metal oxide thin films on wafer-level aiming to find materials for miniaturized gas sensors. Radial dependency of thickness and electrical resistance was investigated by spectroscopic ellipsometry and four-point-probe measurements to reveal film homogeneity over the wafer. An innovative two-side trenched silicon shadow mask was used for layer structuring. In gas measurements the resistive response of the layers to gas atmospheres was investigated and compared. Carbon monoxide in concentrations of several ppm was used as a first model gas for emissions from test fires. Indium oxide and tin oxide showed good sensitivity and short response time.

4H-SiC MOSFETs with a Stable Protective Coating for Harsh Environment Applications

In this work we present 4H-SiC metal-oxide-semiconductor field-effect transistors (MOSFETs) with a stable protective coating for harsh environment applications. Both inversion channel (IC) and buried channel (BC) MOSFETs were realized on n-4H-SiC substrates with a p-epilayer. Stacked ONO gate dielectric and Ti/TiN/Pt/Ti interconnect were used. Ni and Ti ohmic contacts in combination with a-SiOx/a-SiNy and a-SiOx/a-SiC protective coatings were compared. The MOSFETs showed excellent transistor characteristics up to 600 °C and exceptional stability during long-term aging at 600 °C in air and during accelerated aging at 700 °C including temperature cycling and air/moisture environment.

Comparative Study on Metallization and Passivation Materials for High Temperature Sensor Applications

We investigated the performance of different metallization/passivation systems for high temperature applications. The metallizations comprised a 150 nm sputtered Pt or a 150 nm e-beam evaporated PtRh layer on Ti/TiN underlayers, respectively. The passivation coatings consisted of amorphous PECVD SiOx, of amorphous stress-reduced PECVD SiNy, and of a SiOx/ SiNy stack. For samples with SiOx and SiOx/ SiNy passivation layers the electrical properties changed after a short high temperature anneal at 600 °C but then remained stable during further annealing. This was attributed to the formation of PtTi alloys, which stabilized the metallization stack. In samples with SiNy passivation a significant Pt out-diffusion into the passivation layer was observed. This led to a degradation of the electrical and mechanical properties. The best performance was achieved with Pt-based metallizations and SiOx or SiOx/SiNy passivations.

Multiphysics investigation of gas sensor packages

A miniaturized ozone gas sensor working with UV-light was investigated and aspects of its heterointegration were reviewed, simulated and analyzed. We analyzed possible interactions of the integration of functional optical elements together with MEMS-based physical sensors. Gas diffusion into the package and light propagation inside the package were simulated amongst well-known simulations such as heat distribution in the package. As a result of this investigation design constraints and methodology to realize such integration are showed in this paper. Suggestions for technology and component arrangement are given in order to guarantee proper performance of the integrated sensors.