Nathalie Mathieu

Low-frequency noise sources in polysilicon emitter BJT's: influence of hot-electron-induced degradation and post-stress recovery

The noise properties of polysilicon emitter bipolar transistors are studied. The influences of the various chemical treatments and annealing temperatures, prior and after polysilicon deposition, on the noise magnitude are shown. The impact of hot-electron-induced degradation and post-stress recovery on the base and collector current fluctuations are also investigated in order to determine the main noise sources of these devices and to gain insight into the physical mechanisms involved in these processes. >

Highly sensitive Hall sensors

High-performance InGaAs/InAlAs/InP Hall sensors with high magnetic sensitivity, good linearity, low temperature coefficient and high resolution are reported. These sensors use the properties of a two-dimensional electron gas and the benefit of pseudomorphic material, in which both the alloy composition and the built-in strain offer additional degrees of freedom for band structure tailoring. With the described growth optimization of pseudomorphic heterostructures by molecular beam epitaxy, a high electron mobility of 13 000 at room temperature has been obtained. A physical model of the structure including a self-consistent description of the coupled Schrodinger and Poisson equations has been developed to better understand the influence of the design of the heterostructure on its electronic properties. These results have been used in order to optimize the structure design. A magnetic sensitivity of with a temperature coefficient of between and has been obtained, and high signal-to-noise ratios corresponding to minimal magnetic field of at 100 Hz and at 1 kHz have been measured.

Low frequency noise in Schottky barrier contacts of titanium nitride on n-type silicon

The electrical characteristics and the low frequency noise of Schottky contacts on n-type Si(100) have been systematically measured. The thin films were deposited by reactive magnetron sputtering at room temperature. Based on a model of a parallel combination of an ideal diode of current and a generation-recombination diode of current , we have extracted the contribution of both diodes to the measured total current I. Treating the two components and as different noise generators, we have analysed the observed white noise at high frequencies and the excess current noise at lower frequencies. The white noise is explained by using a pure shot noise for the component , by applying Guptas general theorem on noise in non-linear driven devices for the component and by considering an additional noise generator with a Nyquist-type intensity. The excess current noise is explained by a model based on fluctuations of the generation-recombination current only. Analysis of the versus I data allowed us to determine the interface state density.

Low‐frequency noise sources in polysilicon emitter bipolar transistors: Influence of hot‐electron‐induced degradation

The noise properties of polysilicon emitter bipolar transistors are studied. The influences of the various chemical treatments and annealing temperatures, prior and after polysilicon deposition, on the noise magnitude are shown. The impact of hot‐electron‐induced degradation and post‐stress recovery on the base and collector current fluctuations are also investigated in order to determine the main noise sources of these devices.

A new method for the determination of the channel length reduction in polysilicon thin film transistors (TFTs)

The accurate knowledge of the effective channel length in a polysilicon thin film transistor (TFT) is of great importance. The reduction AL of the channel length is due to lateral diffusion from the source and drain contacts into the gate region. The usual method for determining AL is based on plotting the straight line I/I D versus length mask L∞ in the linear region and extrapolating the straight line to intersect the x-axis. We show that this method is approximate and leads to an underestimation of the reduction channel length due to the existence of the access resistance. We propose an alternative method based on the saturation current I Dsat using the 1// Dsall versus L m plots. We show that this method is more accurate especially when the access resistance of the device is important. The extracted parameters ΔL for n- and p-channel polysilicon TFTs are more compatible with the device performance.

Simulation and 3D Characterization of Microsystems

To add more functionalities to microelectronic circuits, microsystems offer growing number of applications. An advanced practical work that combines simulation and optical characterization of microsystems is presented in this paper. It emphases through simulation and characterization results the different characteristics of some of the most utilized microsystems.

Micro-system process for education: fabrication of a pressure sensor

Micro-systems technology is a fast developing field that takes advantage of the well established Si microelectronics technology. In this paper we present the concepts and process flow of the technological elaboration of a pressure sensor. This approach places the emphasis on the key technologies of micro-systems and includes the use of double face photolithography as well as bulk micro-machining. It also benefits standard clean room equipment.

Micro-system process for education: morphological and electrical characterization

An advanced practical work in characterization of microsystems for education is presented. It concerns the measurements of morphological and electro-mechanical properties of a pressure sensor consisting of piezoelectric poly-Si gauges on a membrane. A variety of techniques is used during the fabrication in a clean room, to control the process and characterize the materials (SiO/sub 2/, poly-Si). After complete processing, the sensitivity of the pressure sensor is determined. The influence of the doping, annealing and thickness of the poly-Si gauge is derived. This initiation is developed for the terminal year students of the Grenoble National Engineering School of Electronics (ENSERG) and the Grenoble National Engineering School in Physics (ENSPG).

Surface Micromachining and Electrical Characterization of Polysilicon Microcantilevers

The surface micromachining and the electrical characterization of polysilicon microcantilevers are presented as practical works, conceived as an introduction to MicroElectroMechnicalSystems (MEMS), for students in electrical engineering at the National Polytechnic Institute of Grenoble, France. The aim of these practical works is to illustrate the total compatibility of sensor and actuator technology with MOS integrated circuits.