M. Mozek

The role of Triton surfactant in anisotropic etching of {1?1?0} reflective planes on (1?0?0) silicon

Etching characteristics and properties of {1 1 0} silicon crystal planes used as 45° optical mirrors for deflecting optical beams from/to optical fibers were investigated. Fiber aligning grooves and passive mirror-like planes were realized by wet micromachining of (1 0 0) silicon in KOH–IPA and TMAH–IPA systems. Implementation of Triton-x-100 surfactant as an additive to 25% TMAH in anisotropic etching of {1 1 0} silicon passive mirror planes is reported and discussed. It was found that Triton-x-100 contents in the range of 10–200 ppm to the 25% TMAH–water etchant significantly increase the anisotropy mostly by decreasing the {1 1 0} etch rate and retaining the {1 0 0} etch rate. It is also shown that {1 1 0} surface roughness is substantially improved compared to two other etching systems. Furthermore, efficient convex corner underetching reduction is demonstrated. The results of optical characterization of passive mirrors with 632 nm incident light show reduced scattering of reflected optical beam due to improved microroughness for mirrors made by TMAH–Triton. For the reflection of the optical beam with 1.33 µm and 1.54 µm wavelengths, sputtered layer of gold is used as reflective coating on silicon mirrors thus increasing the reflected optical beam intensity by an additional 8%.

Different aspect ratio pyramidal tips obtained by wet etching of (100) and (111) silicon

Different approaches to obtain sharp silicon tips with a variety of aspect ratios, for potential use in advanced microelectronics applications, were studied. Tips suited for atomic force microscopy and field emission arrays were formed by wet chemical etching of (100) and (111) single crystal silicon in KOH, TMAH and HNA etchant. Apex sharpening with thermal oxidising step resulted in tips with apex radius below 20 nm as evaluated by SEM analysis. The fabrication of silicon tips with isotropic etching on either (100) or (111) silicon confirmed that uniformity across the wafer and tip sharpness are lower with respect to anisotropically etched structures. Pyramidal tips with aspect ratios between 0.5 and 1.2 were obtained by these methods.

Packaging technologies for pressure‐sensors

Pressure‐sensor miniaturization requires high‐density packaging. This means that designers are constantly faced with all kinds of challenging, and sometimes impossible, requirements. In this paper we will present three examples with specific technologies and aspects of miniaturization and packaging. The first example is a pressure switch, the second a pressure sensor and the third a smart pressure sensor.

Temperature effects modeling in silicon piezoresistive pressure sensor

Temperature effects and compensation for temperature drift of offset voltage in silicon piezoresistive pressure sensors were analyzed. The derived equations take into account temperature dependences, the piezoresistive effect and thermal expansion of the diaphragm inducing additional stresses. Measurements performed on fabricated sensors confirm the importance of diaphragm induced thermal stress. Accordingly, a computer program enabling fast calculation of sensor sensitivity and offset voltage was conceived. Based on the analysis, an approach to compensation for temperature drift of offset voltage is proposed and confirmed with experimental results.

Calibration and error correction algorithms for smart pressure sensors

The essential properties of smart sensor error correction algorithms and calibration procedures according to the IEEE1451.2 standard are presented. Using a modern microcontroller design, it is possible to implement STIM in a single chip design, but due to complexity of error correction and calibration algorithms it is preferable to distribute these tasks between several processors available in a network. A description of a simple calibration algorithm intended for implementation in modular STIM (smart transducer interface module) design is given. Other calibration and error correction approaches were tested on designed and fabricated smart sensor networks. Their implementation is discussed and the results of the most promising bivariate spline approximation algorithm are presented.

Characterization of integrated thin film Pt heater and temperature sensors on Si platform

In this paper the design, fabrication methods and characterization of thin film meandered Pt resistive heater (size 20 × 20 mm2) with integrated Pt sensors on Si platform is presented. Pt heaters and temperature sensors were fabricated simultaneously by DC sputtering method. It was found that the fabrication process has significant influence on the electrical properties of the realized thin film resistive layers, which also explains the discrepancies between the calculated and measured values that were obtained during this work. Annealing temperature of the Pt layers was found to influence significantly the final resistance of the deposited layer and was performed at 500°C. To reduce the heat loss, the heater and temperature sensors were covered by Pyrex glass with prefabricated cavity. By this new approach, the power consumption was reduced due to improved thermal insulation. A comparative study was performed and showed that we can decrease the power consumption by more than 25% only by this approach. Measured temperature coefficient of resistance (TCR) for temperature sensors and the heater was between 1400-1700 ppm and showed that also the heater can be used as temperature sensing element.

Effect of gamma irradiation on characteristics of FOXFET biased edge-on silicon strip detector

Edge-on silicon strip detectors were designed and fabricated. The dependence of main detector parameters of importance such as leakage current, dynamic resistance of integrated FOXFET biasing structure, and radiation hardness on ionizing irradiation was investigated. Irradiation tests were carried out at different gate electric field using Co/sup 60/ gamma-ray source up to 0.2 Mrd(SiO/sub 2/). Optimized low-temperature segregation anneal results in a substantial decrease of detector leakage current. Dynamic resistance as high as 2 G/spl Omega/ was achieved on nonirradiated detectors for channel width and length of 10 /spl mu/m. Main factors influencing the radiation hardness of strip detector with FOXFET biasing structure are leakage current and strip potential. Leakage current increases detector noise and lowers the dynamic resistance of FOXFET biasing structure. The strip voltage shift toward positive voltages shows a strong dependence on gate electric field applied during the irradiation. The radiation hardness of oxide and composite nitride/oxide dielectric layers in MIS capacitor structures was investigated. Composite nitride/oxide (MNOS) capacitors show improved radiation hardness compared to oxide (MOS) capacitors in case of applied positive gate electric field.

Compact BJT/JFET PTAT

Research on a new compact BJT/JFET PTAT temperature sensor structure is reported. Equations describing sensor response are derived. The effects of important structure parameters are included. Measurements on fabricated test PTAT structures revealed reasonably good temperature response in a wide temperature range (-130/spl deg/C to +100/spl deg/C). At low temperatures (measured down to -200/spl deg/C), considerable deviation from ideal PTAT response was detected. It is shown that deviation is due to the reduction of constant diode ideality factor n region, related to the free carriers freeze-out effect. JFET current generators, in spite of appreciable temperature dependence, do not include excessive nonlinearity.

Design of transdermal drug delivery system with PZT actuated micropump

Investigation of transdermal drug delivery system, based on silicon injector chip with silicon microneedles and PZT (lead zirconate titanate) actuated micropump, for drug delivery such as insulin is reported. First, basic skin properties and dosing requirements are reviewed. Next, the whole system and its components (injector chip, micropump, drug container) are discussed. Based on this, microneedles injector chip design is discussed and prototypes fabricated. Then, design of PZT actuated micropumps is discussed and prototypes fabricated. From measurements on fabricated micropumps, fluidic parameters are evaluated. Basic requirements for drug container, control electronics and power supply parameters are also presented. Finally, maximum drug delivery, based on measured prototype micropump parameters, through the prototype injector chip is determined.

Microfluidic platforms realized by micromachining and anodic bonding of Si and glass substrates

Presented work focuses mainly on issues accompanied with defect free anodic bonding of multilayer glass-Si-glass microfluidic structures. The problems associated with prefabricated structures which included micromachined or patterned topography on one or both of the mating surfaces and bonding to SiO2 terminated Si were investigated. In this study, Pyrex 7740 and Borofloat 33 glass wafers were bonded to bare Si and Si/SiO2 terminated structures in the temperature range 350-400°C in the air ambient under applied anodic voltages between 800-1200V. Appropriate configuration of bonding electrodes was found mandatory to avoid debonding effects in multilayer bonding process. Wet etching of glass was used to fabricate microchannels and recessed structures in glass, which were subsequently anodically bonded to the cover glass via different intermediate layers. Thin intermediate Al layer was found to provide very uniform and stable bond between two glass wafers.