M. Ádám

Modification of Al/Si interface and Schottky barrier height with chemical treatment

The influence of different chemical treatments on the electrical behaviour of n- and p-type Al/Si Schottky junctions was studied. A Schottky barrier height of 0.91 eV was achieved on p-type Si probably due to the unpinning of the Fermi-level at the Al/Si interface. This is one of the highest barrier height values reported so far for a solid-state Schottky junction prepared to p-Si. A doping level reduction was observed in the vicinity of the Si surface for wafers with native oxide and for those boiled in acetone or annealed in forming gas. It was observed unexpectedly that the reactive plasma etch used for the formation of mesa structures decreases the apparent Schottky barrier height. The relation between the sum of n- and p-type Schottky barrier heights and forbidden gap is discussed.

Materials and processing for realization of micro-hotplates operated at elevated temperature

Micro-pellistors and conductivity-type gas sensors are among the most promising candidates for the monolith integration of gas-sensing elements in olfactory gas detection. Both types have to be operated at elevated temperatures of 200–600 °C; therefore, the formation of thermally isolated integral micro-hotplates is the key element in the development of the array. In this paper, the alternative processes are discussed with emphasis on thermal isolation, selection of the appropriate structural materials, formation of stable contacts to the filaments and deposition of gas-sensitive layers. The results of thermal and mechanical model calculations were confirmed by experimental measurements.

Characterization of an Integrable Single-Crystalline 3-D Tactile Sensor

Porous-Si-micromachining technique was used for the formation of single-crystalline force-sensor elements, capable of resolving the three vector components of the loading force. Similar structures presented so far are created from deposited polycrystalline Si resistors embedded in multilayered SiO2/Si3N4 membranes, using surface micromachining technique for a cavity formation. In this paper, the authors implanted four piezoresistors in an n-type-perforated membrane, having their reference pairs on the substrate in order to form four half bridges for the transduction of the mechanical stress. They successfully combined the HF-based porous-Si process with conventional doping and Al metallization, thereby offering the possibility of integration with readout and amplifying electronics. The 300times300 mum2 membrane size allows for the formation of large tactile arrays using single-crystalline-sensing elements of superior mechanical properties. They used the finite-element method for modeling the stress distribution in the sensor, and verified the results with real measurements. Finally, they covered the sensors with different elastic silicon-rubber layers, and measured the sensors altered properties. They used continuum mechanics to describe the behavior of the rubber layer

Thermal investigation of micro-filament heaters

The present work is a study of the thermal properties of integrable micro-filaments. The realised structure is the key element of the targeted integrable micro-pellistor for catalytic gas sensing, therefore, its thermal characterisation is of crucial importance. Direct measurement of temperature in the micro-heater is unfortunately troublesome due to the small dimensions used. In this work the temperature of the micro-filament was measured by two different methods, based upon the resistance alteration of the filament, and analysis of the thermal radiation of the heated micro-filament. The reason for the differences was explained by inherent features of the methods, and confirmed by thermal simulation.

Efficient catalytic combustion in integrated micropellistors

This paper analyses two of the key issues of the development of catalytic combustion-type sensors: the selection and production of active catalytic particles on the micropellistor surface as well as the realization of a reliable thermal conduction between heater element and catalytic surface, for the sensing of temperature increase produced by the combustion. The report also demonstrates that chemical sensor product development by a MEMS process is a continuous struggle for elimination of all uncertainties influencing reliability and sensitivity of the final product.

Three dimensional single crystalline force sensor by porous Si micromachining

A porous Si micromachining technique was used for the formation of single crystalline force sensor elements, capable of resolving the three vectorial components of the load. Similar structures presented so far, are formed from deposited polycrystalline Si resistors embedded in multilayered SiO/sub 2//Si/sub 3/N/sub 4/ membranes, using a surface micromachining technique for cavity formation. In the present work, in the n-type perforated membrane, four implanted piezoresistors were fabricated with their reference pairs on the substrate, in order to form 4 half-bridges for the transduction of the mechanical stress. The HF based porous Si process was successfully combined with conventional doping and Al metallization, thereby offering a possible integration of read-out and amplifying electronics. The 300/spl times/300 /spl mu/m/sup 2/ membrane size allows the formation of large area arrays for tactile sensing using single crystalline sensing elements of superior mechanical properties.

Ion beam analysis of plasma immersion implanted silicon for solar cell fabrication

Abstract Phosphorus ions were implanted using plasma immersion ion implantation (PII) to create shallow pn junctions in solar cells. Depths of PII phosphorous were shallow enough to be analyzed by Rutherford Backscattering Spectrometry (RBS) combined with the channeling technique. It was shown that PII is able to produce a high enough surface concentration of phosphorous (several times 1021 cm−3) for shallow pn junctions. RBS revealed that after 5 minutes of implantation phosphorus surface concentrations remained almost unchanged due to the balance of implantation and surface sputtering. A heavily damaged layer was found at the surface, the thickness of which was comparable to the range of the co-implanted hydrogen depth profile. Electrical activation of the implanted phosphorus and junction depth measured by Spreading Resistance Profiling (SRP) were favourable for short time PII of about 1–5 minutes.

Noise in piezoresistive Si pressure sensors

The principles of the construction of piezoresistive silicone pressure sensors are outlined. The fabrication of sensors with ion-implantation and common silicone wafer technology is described. The simulation of the devices showed that the membrane thickness has a major influence on the sensitivity, while the misalignment is less important. The low-frequency noise spectra of the piezoresistive elements are Lorenzian; the characteristic time constant is about 23 μs. The bias dependence of the spectra is in some degree less than it was expected from the regular V2 scaling. The plateau of the noise spectrum at working conditions is higher with almost 30 dB than the thermal noise. This excess noise is attributed to a trap level; however the origin of this G-R center is not clear yet. The figures of merits of the sensor were also estimated in numerical examples.

Mats of Functionalized Carbon Nanotubes for Gas/Vapor Sensing

Gas sensing properties of different carbon nanotube (mostly multiwall, MWCNT) mats, based on electrical resistance measurement were investigated in a simple arrangement and found that the sensitivity for different gases or vapors highly depends on the pre-treatment and functionalization of nanotubes. The selectivity of the sensing was demonstrated by building a vapor recognition system based on an array of multitube sensors made of differently functionalized MWCNTs.

Integrated tactile system for dynamic 3D contact force mapping

We present the first integrated tactile system that is based on dynamic, spatially distributed, three-axial contact force data. Compared to general pressure mapping systems, our devices measure not only one, but all three components of contact forces (normal and shear) with up to 64 independent micromachined force sensing elements integrated on a single chip. The spatially distributed shear force sensing adds new dimensions and directions to tactile data analysis, including pre-slip detection, enhanced robotic grasping or high quality tactile texture classification. In this paper we briefly describe the components of the novel system: the sensor arrays, the data acquisition methods and the data analysis software. We also present two example applications that exploit the advantages of real time three-dimensional contact force mapping.