Alain Giani

Design of a micromachined thermal accelerometer: thermal simulation and experimental results

This paper describes numerical simulation of a micromachined thermal accelerometer and experimental measurements. The sensor principle consists of a heating resistor, which creates a symmetrical temperature profile, and two temperature detectors symmetrically placed on both sides of the heater. When an acceleration is applied, the free convection is modified, the temperature profile becomes asymmetric and the two detectors measure the differential temperature. This temperature profile and sensor sensitivity according to the distance heater-detector have been studied using numerical resolution of fluid dynamics equations with the commercial code CFD2000/STORM: it shows that the optimum distance between the temperature detectors and the heater is about 300 μm. A thermal accelerometer with 3 pairs of detectors placed at 100, 300 and 500 μm from the heater was manufactured using the techniques of micromachining silicon and experimental measurements have shown a good agreement with the numerical simulations: the experimental optimum distance between heater and detectors seems to be close to 400 μm and the differential temperature of detectors is about 3 °C/g for an operating heater power of 54 mW and an heater temperature rise AT of 238 °C. The electrical sensitivity is then 2.5 mV/g.

Growth and characterization of metal-organic vapour phase epitaxial Ga1−xInxAsySb1−y quaternary layers

Abstract The growth in the miscibility gap and the characterization of MOVPE Ga1−xInxAsySb1−y quaternary layers have been undertaken. The experimental conditions have been determined to obtain quaternary epilayers in the miscibility gap grown on GaSb with a good morphology even for lattice mismatched layers, in varying ΣPIII and DH2. The material quality has been assessed by single and double X-ray diffraction. The spectral responses of GaInAsSb(p)/GaSb(n) heterojunction are given. A spectral response obtained under illumination from the GaSb side, presents a good response at 2.75 μm.

Frequency response analysis of an accelerometer based on thermal convection

In this work, we present the design and dynamic evaluation of a micromachined thermal accelerometer based on convection. The accelerometer sensitivity and also the bandwidth have been experimentally and numerically studied as a function of the cavity volume, as well as the nature and the pressure of the gas. Although this type of sensor has already been intensively studied, few works on experimental analysis of the frequency response have been published. In particular, no experimental result on frequency response versus the nature of the gas medium and its pressure were reported in the literature. Under specific conditions, a bandwidth greater than 300 Hz was measured without any electronic signal treatment. Computational fluid dynamics simulations were carried out on a model of our device and satisfactory concordance with the experimental results was revealed. Therefore, the effects of the aforementioned parameters such as volume, gas medium and volume of the latter are theoretically, experimentally and numerically investigated.

Investigation of Pt/Ti bilayer on SiNx/Si substrates for thermal sensor applications

Pt/Ti thin films on SiNx/Si substrates have been investigated for thermal sensor applications on SiNx membrane. Therefore, Pt/Ti adhesion during KOH etching of silicon and high temperature coefficient of resistance (TCR) are the principal aims of this study. ac sputtering and electron beam evaporation have been investigated for metal deposition. Vacuum annealing is used to improve the Pt/Ti characteristics. Stress characterizations and adhesion strength are evaluated by an x-ray diffraction pattern and adhesive tape test, respectively. TCR and resistivity were finally measured to confirm the compatibility with good thermal sensor sensitivity. Pt/Ti films elaborated by electron beam evaporation and vacuum annealed present the best characteristics for thermal sensor applications: good adhesion is obtained even after 5 h in KOH etching solution, electrical resistivity is about 15 μΩ cm and TCR is 3.3×10−3/°C. Finally, by using these platinum thin films, a thermal accelerometer has been manufactured and tilt ...

Design of a new sensor for mass flow controller using thin-film technology based on an analytical thermal model

Thermal mass flow controllers are widely used in the semiconductor industry to deliver accurate process gas compositions and concentrations to the processing chamber. The sensor, a stainless-steel capillary tube, is the most critical part of the mass flow controller. We have designed a new sensor using thin-film technology in order to improve its reliability and to decrease its response time. The two temperature sensors are deposited platinum on an electrical insulating layer directly upon the capillary tube (without exposure to the gas stream) whereas the sensor is constantly heated by a resistive wire. The so-obtained sensors are very promising and the new design and technology could give us improvements which the old design and technology (two resistive coils) would not have been able to give us. The physical mechanisms of this new sensor are described by a third-order steady-state analytical thermal model which gives good results when compared with experiments. This fundamental study also includes the...

InGaSb/GaSb photodiodes grown by MOVPE

Abstract We report a systematic investigation of the growth by MOVPE of a series of InGaSb photodiodes lattice-mismatched on GaSb substrates. The samples were grown in two atmospheric pressure MOVPE reactors and with different organometallic sources. We have investigated the use of various intermediate layers between the substrate and the homojunction photodiode such as compositional ramps, steps and superlattices in order to prevent dislocations due to the lattice mismatch from reaching the crucial p/n junction at the top of the device. The top layers have been evaluated by X ray diffraction, SIMS profiling and imaging, Hall and resistivity measurements. From these layers, photodiodes were fabricated with mesa wet etching without any antireflecting coating. Electrical and optical characteristics of these photodiodes — dark current, capacitance and external quantum efficiency — were investigated at room temperature. The dark current and diffusion length are compared with a p/n InGaSb homojunction grown without intermediate layer and with a p/n InGaAsSb homojunction lattice-matched on GaSb.

Optical and electrical characterization of thick GaSb buffer layers grown on 2 in GaAs wafers

Abstract We have investigated the growth of thick, highly uniform GaSb buffer layers on 2 in GaAs substrates. We have found that ramping the temperature under an arsine flux optimizes the switching sequence between GaAs and GaSb. In this case, the large (about 8%) lattice mismatch which separates the GaAs and GaSb bond lengths is abruptly relaxed, and good quality GaSb can be homogeneously deposited. On such samples, the photoluminescence signal ranks as well (or even better) as that obtained for comparative homoepitaxial material; also, the electrical properties are among the best ever reported for GaSb grown by metal-organic chemical vapor deposition on GaAs.

Effect of the Detector Width and Gas Pressure on the Frequency Response of a Micromachined Thermal Accelerometer

In the present work, the design and the environmental conditions of a micromachined thermal accelerometer, based on convection effect, are discussed and studied in order to understand the behavior of the frequency response evolution of the sensor. It has been theoretically and experimentally studied with different detector widths, pressure and gas nature. Although this type of sensor has already been intensively examined, little information concerning the frequency response modeling is currently available and very few experimental results about the frequency response are reported in the literature. In some particular conditions, our measurements show a cut-off frequency at −3 dB greater than 200 Hz. By using simple cylindrical and planar models of the thermal accelerometer and an equivalent electrical circuit, a good agreement with the experimental results has been demonstrated.

First high-g measurement by thermal accelerometers

In the present work, the design and experimental set-up conditions of a micromachined accelerometer based on convection heat transfer are reviewed. The effects on sensitivity are analytically studied and allow discussion of the linearity range. They are confirmed by simulation and experimental results. With optimized experimental parameters, we achieve for the first time high-g measurements of up to 10,000 g with a thermal accelerometer.

Lateral growth on GaSb(111)B and GaSb(001) by metal-organic chemical vapour deposition

Abstract The study of lateral growth by metal-organic chemical vapour deposition (MOCVD) techniques is expected to yield information concerning the growth mechanisms of MOCVD. In the case of growing layers delimited by mask windows, the undesirable effect of lateral growth must be avoided as far as possible. However, it has appeared that lateral growth cannot be avoided, and therefore the shape of the device window is evaluated in order to take into account and to minimize this effect, or on the contrary to profit from it. In this paper we describe the growth behaviour of Ga0.64In0.36Sb by MOCVD on the surface and from the side walls of pedestals coated or not coated with SiO2. The GaSb substrates are (111)B or (001) oriented. On B(111) substrates the lateral growth rate is maximum in the 〈112〉A direction and minimum in the 〈112〉B direction. On GaSb(001) substrates, the lateral growth rate is maximum in the 〈110〉 direction and minimum in the 〈1 1 0〉 direction.