The essential role that Si atoms emitted from the interface play in determining the silicon-oxidation rate is theoretically pointed out, and a universal theory for the oxide growth rate taking account of the interfacial Si-atom emission is developed. Our theory can explain the oxide growth rate for the whole range of the oxide thickness without any empirical modifications, while the rate for an oxide thickness of less than 10 nm in dry oxidation cannot be explained with the Deal-Grove theory.

We have determined silicon self-diffusivity at temperatures 735-875 degrees C based on the Raman shift of longitudinal optical phonon frequencies of diffusion annealed 28Si/30Si isotope superlattices. The activation enthalpy of 3.6 eV is obtained in such low temperature diffusion annealing. This value is significantly smaller than the previously reported 4.95 eV of the self-interstitial mechanism dominating the high temperature region T>>855 degrees C and is in good agreement with the theoretical prediction for the vacancy-mediated diffusion. We present a model, containing both the self-interstitial and the vacancy terms, that quantitatively describes the experimentally obtained self-diffusivity between 735 and 1388 degrees C, with the clear crossover of the two diffusion mechanisms occurring around 900 degrees C.

Boron (B), phosphorus (P), and arsenic (As) in-diffusion profiles were simulated based on an integrated diffusion model that takes into account the vacancy mechanism, the kick-out mechanism and the Frank–Turnbull mechanism. The simulations were done using just three parameters for B and P, and four parameters for As, each of which has a clear physical meaning and a physically reasonable value, with no additional ad hoc hypothesis. These parameters correspond to the diffusion of dopant species and of point defects that contribute to dopant diffusion. For the anomalous P diffusion profile, the vacancy mechanism governs the diffusion in the plateau region, while the kick-out mechanism governs it in the deeper region, where self-interstitials dominate in the kink region and P interstitials dominate in the tail region. This changeover from the vacancy contribution to the kick-out contribution is shown to be the mechanism for the appearance of the kink-and-tail profiles of P. Moreover, the comparison among B, P, and As diffusion is made to review the diffusion of these three dopants by means of a unified model.

Silicon oxidation in wet ambients is simulated based on the interfacial silicon emission model and is compared with dry oxidation in terms of the silicon-atom emission. The silicon emission model enables the simulation of wet oxidation to be done using the oxidant self-diffusivity in the oxide with a single activation energy. The amount of silicon emission from the interface during wet oxidation is smaller than that during dry oxidation. The small emission rate for wet oxidation is responsible for the insignificant initial oxidation enhancement and the linear pressure dependence of the oxidation rate observed in wet oxidation. Using a unified set of parameters, the whole range of oxide thickness is fitted for both (100) and (111) substrates in a wide range of oxidation temperatures (800 °C–1200 °C) and pressures (1–20 atm).

Structural relaxation and self-diffusion in covalent amorphous solids: Silicon nitride as a model system

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We have simulated silicon oxidation taking into account the emission of a large number of silicon atoms from the interface, which governs the silicon-oxidation rate. The silicon emission model enables the simulation to be done using the oxidant self-diffusivity in the oxide with a single activation energy. The simulation has deduced a silicon emission rate that exhibits a break point in its activation energy at around 1000°C, which is attributed to the viscoelastic properties of the oxide. Using a unified set of parameters, the whole range of oxide thickness is fitted in a wide range of oxidation temperatures (800–1200°C) without any empirical modifications.

Wearable sensor device technologies, which enable continuous monitoring of biological information from the human body, are promising in the fields of sports, healthcare, and medical applications. Further thinness, light weight, flexibility and low-cost are significant requirements for making the devices attachable onto human tissues or clothes like a patch. Here we demonstrate a flexible and printed circuit system consisting of an enzyme-based amperometric sensor, feedback control and amplification circuits based on organic thin-film transistors. The feedback control and amplification circuits based on pseudo-CMOS inverters were successfuly integrated by printing methods on a plastic film. This simple system worked very well like a potentiostat for electrochemical measurements, and enabled the quantitative and real-time measurement of lactate concentration with high sensitivity of 1 V/mM and a short response time of a hundred seconds.