This paper examines the process of anodic bonding with regard to the fabrication of silicon-glass capacitive sensors. Various glasses are assessed in terms of the suitability of their physical properties and results are presented on flatness control of these glasses when bonded to silicon at different temperatures. Many of the problems which can typically affect silicon-glass sensors are examined and explained in terms of the anodic bonding process. Effects such as the electrolysis of the glass and the transport of the oxygen produced in this process are discussed and design considerations for minimising deleterious effects of this oxygen are presented. We demonstrate the process of selection of glass, bonding parameters and other material selection by reference to a device on which we are currently working.

Selection of glass, anodic bonding conditions and material compatibility for silicon-glass capacitive sensors

https://cyberleninka.org/article/n/1497549.pdf

Atomic diffusion induced degradation in bimetallic layer coated cemented tungsten carbide

The basic objective of this work was to investigate a suitable ohmic metallization to 3C-SiC epitaxial layer with relatively low process temperature, which is important for on-chip circuit integration. In this study, the ohmic contacts are associated with the catalytic-metal/SiC Schottky diode gas sensors operable at 400 °C. Therefore, the contacts must be reliable for efficient operation of the sensors at this temperature in air ambient. Several metallization schemes were studied and the observed electrical characteristics were correlated to the interface properties by secondary ion mass spectrometry. Nickel contacts to moderately doped (∼10 17 cm −3 ) 3C-SiC epilayer did not exhibit linear current–voltage relationship even after annealing at 600 °C. On the other hand, aluminum exhibited considerably low intercontact resistance in the as-deposited condition. But with increase in annealing temperature the current flow between a couple of Al contacts was impeded presumably due to very high affinity of this metal for oxygen. Titanium exhibited good ohmic properties after annealing at 400 °C. However, higher temperature (600 °C) annealing in air ambient (intended to examine its stability limit) caused surface oxidation of the Ti layer. This problem was minimized by deposition of 100 nm Au overlayer (on top of 400 nm Ti) which would increase the surface conductivity of the ohmic contacts and ensure stable wire bonding.

Ohmic contacts to 3C-SiC for Schottky diode gas sensors

A study on the energy injection-induced damage, by a pulse-modulated RF signal source, to a silicon bipolar low-noise amplifier (LNA) is described in this paper based on the analysis of pre- and post-injection data of the noise figure and the gain. Experimental results show that both the noise and the gain characteristics of the LNA are sensitive to energy injection. Sample dissection analysis and simulation results also indicate that energy injection damages the base electrode, and thus causes the base resistor to increase, and, as a result, leads to an increase of the LNA noise. However, the gain of most LNA samples increases with the injection energy level following the time-based drift failure model of the bipolar current gain hFE. It is found that using the gain characteristics difference prior to and after the injection as the sole parameter to evaluate the damage is insufficient due to the complexity of the effect of energy injection-induced damage.

The effect of injection damage on a silicon bipolar low-noise amplifier

The interaction at the interface between chromium and amorphous Silicon (a-Si) films in the presence of a sandwich layer of chromium oxide is investigated using X-ray absorption fine structure (XAFS) spectroscopy. The oxidized interface was created, in situ, prior to the deposition of a 400 nm tick a-Si layer over a 50 nm tick Cr layer. The entire stack of substrate/metallic Cr/Cr2O3/a-Si was then annealed at temperatures from 300 up to 700 °C. Analysis of the near edge and extended regions of each XAFS spectrum shows that only a small fraction of Cr is able to diffuse through the oxide layer up to 500 °C, while the remaining fraction is buried under the oxide layer in the form of metallic Cr. At higher temperatures, diffusion through the oxide layer is enhanced and the diffused metallic Cr reacts with a-Si to form CrSi2. At 700 °C, the film contains Cr2O3 and CrSi2 without evidence of unreacted metallic Cr. The activation energy and diffusion coefficient of Cr are quantitatively determined in the two temperature regions, one where the oxide acts as diffusion barrier and another where it is transparent to Cr diffusion. It is thus demonstrated that chromium oxide can be used as a diffusion barrier to prevent metal diffusion into a-Si.

Benda Yan

Papers

Interdiffusion of an Au/Ni/Cr multilayer metallization on silicon substrates