Z. Lazic

Vacuum MEMS sensor based on thermopiles - simple model and experimental results

This paper presents a simple model of MEMS thermopile based vacuum detector and experimental results obtained for sensors designed and fabricated at IHTM-IMTM. Sensors contain two thermopiles, each with 30 multilayer p+Si/Al thermocouples and p+Si or Al heater. Thermal isolating membrane has sandwich structure consisting of sputtered SiO2 and residual n-Si layer. Dependence of output thermopile voltage on pressure was measured for sensors with different membrane thickness. Tests were performed in pressure range (10-3-105) Pa. Experimental results were compared with theoretical predictions.

Multipurpose thermal sensor based on Seebeck effect

This paper reports a multipurpose thermal sensor based on the Seebeck effect. The sensor has thermocouples with a multilayer structure consisting of one thermocouple strip laying on the insulating membrane and the other one under the first thermoelement and the membrane. The vertical arrangement allows a greater number of thermocouples to be placed on a given chip area. Central and lateral thermistors are placed near hot and cold thermocouple junctions, respectively, and serve for determination of the temperature difference established on the chip. Experimental results confirm that the same structure could be used as a thermal converter and a gas flow meter.

Numerical calculation of photodetector response time using Ramo's theorem

The work presents a methodology for numerical calculation of response time of p-i-n photodiodes using the corpuscular approach, i.e. the Ramos theorem. The calculations were performed for the Si p-i-n photodiode homostructure which is now already standard and for a high-speed InP-InGaAs-InP photodetector heterostructure. The results show a good agreement with the results obtained using the usual collective approach, however in our calculation the numerical calculation is significantly simplified, and the physical presentation of the process is extremely simple.

Intelligent industrial measurement instruments with silicon piezoresistive MEMS pressure sensors

In this paper we first describe the latest silicon piezoresistive MEMS pressure sensor developed and manufactured at the Center of Microelectronic Technologies (ICTM-CMT). We introduce the concept of intelligent industrial instrumentation, and present a method that enables simultaneous high-performance pressure and temperature measurement to be realized using the described sensor. Experimental verification of the method was performed using the intelligent industrial instrument platform developed at ICTM-CMT. The obtained results have been discussed. They indicate that it is possible to meet or exceeded the measurement performance of existing industrial-grade equipment by using the described approach. An important advantage of the method is that it can enable the temperature measurement capability to be added to some existing intelligent transmitters without hardware modifications. A new intelligent industrial liquid level transmitter, based on the described method and developed at IHTM-CMT, is also presented.

Influence of impurity distribution on thermal coefficients of resistivity and piezoresistivity of diffused layers in silicon

This work presents a numerical investigation of impurity distribution changes caused by technological parameters variations and their influence on thermal sensitivity of piezoresistive pressure sensors. It is shown that the ratio of thermal coefficients of resistivity and piezoresistivity for a sensor may be optimized by a proper choice of process parameters. In this way the conditions are provided for simple passive temperature compensation. The goal of this work was to give a simplified and quick procedure for numerical prediction of the impurity profiles corresponding to optimum values of thermal coefficients of silicon pressure sensors. Contrary to the generally accepted theory, it was shown that the thermal coefficients depend not only on the impurity concentration on the surface, but on their distribution near the surface as well, which can be used in practical optimization of these coefficients.

Helium sensing using multipurpose thermopile-based MEMS devices

In this paper gas sensing performance of IHTM thermopile-based MEMS sensors is studied both theoretically and experimentally. The sensor has already been proven to be a multipurpose device and this work explores possibilities of broadening of its field of application towards gas sensing. Simulation data are given for the study of gas type and binary gas mixture composition detection. Experimental results considering air and helium detection are in good agreement with theoretical predictions.

Boron Redistribution During SOI Wafers Thermal Oxidation

We fabricated silicon-on-insulator (SOI) pressure sensors intended for operation in a wide temperature range. After the thermal oxidation process, the measured sheet resistance of the silicon active layer was higher than expected for the case when the dopant distribution in the active layer is uniform and the layer thickness reduced. The reason was the redistribution of dopant (boron) in the active layer during the high temperature thermal oxidation processes. We developed a model to calculate the boron redistribution in an SOI wafer which was initially uniformly doped. The temperature dependence of hole mobility (and, based on it, the sheet resistance and its temperature dependence) was determined for a calculated impurity profile after oxidation in wet O 2. The experimental temperature dependence of sheet resistance was obtained by measuring the temperature dependence of piezoresistor resistance. The best match between the theoretical and experimental TCR (temperature coefficient of resistance) was achieved by slightly modifying the Aroras model for hole mobility

Glass micromachining with sputtered silicon as a masking layer

In this work we present the not so commonly use of RF sputtered silicon as a masking layer for glass wet etching. The main advantages of this technique are low deposition temperature of silicon layer compared to PECVD and LPCVD processes, simplicity to use and low cost. Si layers were sputtered on 2.5×2.5cm2 Pyrex 7740 substrates. The measured thickness of deposited silicon layer was 2.2μm. Silicon layer was patterned using lift-off technique. Etching was done in undilluted HF (49%) with estimated etch rate of ~8μm/min. Good quality of the glass surface without pinholes and notch defects on the glass etched edges suggests that using sp-Si layer as a masking material for glass etching is feasible.

A measurement setup enabling automatic characterization of silicon piezoresistive MEMS pressure sensors

In this paper a measurement setup is presented that enables automatic characterization of silicon piezoresistive MEMS pressure sensors. It is used for determination of the pressure and temperature dependences of sensor electrical parameters. Some of the equipment in the setup, and the software application that controls the process, are developed at the Center of Microelectronic Technologies (CMT). The main objective of the work is to make the sensor characterization experiment as efficient as possible, without sacrificing measurement performance. An example of obtained measurement results is given for 3 sensors fabricated at CMT. The work greatly facilitates small series production of pressure sensors and instruments, as well as research activities in the field of pressure sensors at CMT.

Gradient-index infrared metamaterials based on metal-dielectric submicrometer pillar arrays

This paper presents the design and microfabrication of a two-dimensional metal-dielectric metamaterial structure based on an array of pillars with submicrometer diameters and heights. The diameters of pillars periodically vary along one axis in a sawtooth fashion and are constant along the other. The electromagnetic field distribution within this graded metamaterial was considered utilizing an accurate analytical approach. The pillar arrays were fabricated in photoresist and subsequently covered with a sputter-deposited aluminum film. Structures were defined by direct laser writing in photoresist film. Controlled overexposure has been applied in order to make pillar features smaller than the nominal resolution of the equipment. The structures were characterized by optical and atomic force microscopy and by angle-dependent Fourier Transform infrared spectroscopy. The produced graded frequency-selective surfaces may be used e.g. in sensing.