M. Zen

Development of ISFET array-based microsystems for bioelectrochemical measurements of cell populations

Monitoring the bioelectrochemical activity of living cells with sensor array-based microsystems represents an emerging technique in a large area of biomedical applications, ranging from basic research to various fields of pharmacological analyses. The main appeal is the ability of these miniaturised microsystems to perform, in real time, non-invasive in-vitro investigations of the physiological state of a cell population. In this paper, we present two different microsystems designed for multisite monitoring of the physiological state of a cell population. The first microsystem, intended for cellular metabolism monitoring, consists of an array of 12 spatially distributed ISFETs to detect small pH variations induced by the cell population. The second microsystem consists of an array of 40 ISFETs and 20 gold microelectrodes and it has been designed to monitor the electrical activity of neurons. This is achieved by direct coupling of the neuronal culture with the ISFET sensitive layer and by utilising gold microelectrodes for neuronal electrical stimulation.

Gas sensing through thick film technology

Abstract We report in our research on semiconductor-based sensing layers deposited via thick-film technique. Particular focus was devoted to achieve nanosized films through proper processing and to study their morphological and structural features. Nanosized powders were prepared by sol–gel method or laser-assisted spray pyrolysis. We also considered some techniques to maintain the stability of a nanostructure for long-term usage of the sensing layers. We detailed the preparation of screen printing pastes suitable for gas sensing application. Implementation of the sensing film on a low-power-consumption micromachined hotplate has also been addressed. The performance of such devices is presented and compared to that of conventional units.

Development of a low-power thick-film gas sensor deposited by screen-printing technique onto a micromachined hotplate

Abstract We report on the design, implementation and characterisation of a thick-film gas sensor deposited for the first time by screen-printing technique onto a micromachined hotplate, the microheater maintains a film temperature as high as 400°C with 2 was achieved by computer-aided screen-printing. The films were then fired through the microheater itself to guarantee thermodynamic stability for long time exploitation. The response of the device to CO, CH 4 and NO 2 at concentrations typical for indoor and outdoor applications was recorded by measuring the film resistance through ultra high impedance CMOS circuit.

Development of a fabrication technology for double-sided AC-coupled silicon microstrip detectors

Abstract We report on the development of a fabrication technology for double-sided, AC-coupled silicon microstrip detectors for tracking applications. Two batches of detectors with good electrical figures and a low defect rate were successfully manufactured at IRST Laboratory. The processing techniques and the experimental results obtained from these detector prototypes are presented and discussed.

SILICON PIN RADIATION DETECTORS WITH ON-CHIP FRONT-END JUNCTION FIELD EFFECT TRANSISTORS

Abstract We report on the latest results obtained from the development of a fabrication technology for PIN radiation detectors with on-chip front-end junction field effect transistors (JFETs) integrated on high-resistivity, FZ silicon. P-doped polysilicon back-side gettering prevented carrier lifetime degradation in spite of the relatively high thermal budget characterizing the fabrication process, allowing very low leakage currents ( ≃1 nA/cm 2 at full depletion) to be obtained. Results from JFETs electrical characterization are presented, showing high transconductance and output resistance values as well as low gate currents and input capacitance. JFETs performance is not affected by the high reverse-bias voltage required for detector operation, making these devices suitable for the fabrication of monolithical preamplifiers integrated on the detector chip.

Polysilicon mesoscopic wires coated by Pd as high sensitivity H2 sensors

A new class of H2 sensors made up of mesoscopic polysilicon wires coated by palladium is presented. Using surface micromachining combined with an usual microelectronic planar process, polysilicon wires of the following dimensions have been constructed: from 250 nm up to 3.7 µm wide, from 100 µm up to 140 µm long, about 700 nm thick. Because of their high surface/volume ratio, these wires have shown a very high resistance percentage variation under hydrogen absorption. Enhanced resolution together with a low production cost are the most important feature of this device.

Sensors Based on Technology “Nano-on-Micro” for Wireless Instruments Preventing Ecological and Industrial Catastrophes

The problem of gas analyzers compatible with wireless networks can be solved by using sensors based on the “nano-on-micro” technology. The basis of this technology consists in nano-composite sensing metal oxide semiconductor or thermocatalytic materials deposited on a microhotplate fabricated using silicon or alumina microelectronic technology. As a result, the sensor combines the advantages of both technologies: on the one hand, high stability and sufficient selectivity of nano-composite materials, and, on the other hand, microprocessor compatibility, low-cost, mass-production possibilities, and low power consumption of microelectronic substrates. Two methods for the fabrication of microhotplates are the most promising: the silicon based technology of silicon oxide/silicon nitride membranes and the CeraMEMS technology of thin alumina films (TAF). The first technology enables the fabrication of microheaters with a power consumption around 20 mW for an operating temperature below 450°C. Advantages of CeraMEMS platforms are: (1) operation at temperature up to 600°C and, potentially, up to 800°C; (2) robustness compared with silicon chip with thin membrane; (3) perfect Pt and sensing layer adhesion without any adhesive layers; (4) low cost of middle scale production (104–107 chips per year) compared with the silicon technology. The CeraMEMS platform can be used for the fabrication of semiconductor and thermocatalytic gas sensors, as a source of IR radiation for optical gas sensors and as bolometers. The sensor withstands ∼7 × 106 on-off cycles. Heater resistance drift is below 3% per year at 550°C.

Experimental study and analysis of corner compensation structures for CMOS compatible bulk micromachining using 25wt% TMAH

In the present work, most common compensation structures ( squares and bars) have been used for convex corner compensation with 25wt% TMAH-water solution at 90+/-1^oC temperature. Etch flow morphology and self-align properties of the compensating structures have been investigated. For 25wt% TMAH water solution {311} plane is found to be responsible for corner undercutting, which is the fast etch plane. Etch-front-attack angle is measured to be 24^o. Generalized empirical formulas are also discussed for these compensation structures for TMAH-water solution. square structure protects mesa and convex corner and is the most space efficient compared to other compensation structures, but unable to produce perfect convex corner as bar type structures. Both the bar structures provide perfect convex corners, but wide bar structure is more space efficient than the thin bar structure. Implications of these compensation structures with realization of accelerometer structure have also been discussed. A modified quad beam accelerometer structure has been realized with these compensation structures using 25wt% TMAH.

An H+-FET-based system for on-line detection of microorganisms in waters

Abstract A flow-through system for on-line detection of microorganisms in waters is presented. A Si3N4 ISFET with integrated signal-conditioning electronics, expressly designed for this application, is employed as an H+ sensor. The article describes the system principles, the transducer architecture, a preliminary characterization of the developed sensor chip, and preliminary measurements performed in the presence of microorganisms.

MOS-junction-based nanostructures by thermal oxidation of silicon wires for hydrogen detection

Heavily p-doped monocrystalline silicon wires have been fabricated by employing isotropic Si wet etch and thermal oxidation to achieve a nanometric cross section-a gate-oxide growth and a final palladium evaporation made up the MOS junction able to detect hydrogen concentration in air. Several types of wire dimensions have been designed and fabricated: length ranges from 5 to 70 /spl mu/m; the smallest widths obtained are around 250-300 nm, while the biggest are up to 7 /spl mu/m. Preliminary experimental results show a high signal/noise ratio sensor response to 100 ppm concentration of H/sub 2/ at room temperature, 1-atm air.