Borut Pečar

Experimental study of heat-treated thin film Ti/Pt heater and temperature sensor properties on a Si microfluidic platform

Design, fabrication and characterization of thin film Ti/Pt heaters and integrated temperature sensors on a Si microfluidic platform are presented. Ti/Pt heaters and sensors provide controlled heating of microchannels realized on the opposite side of the Si platform. Ti/Pt heaters and sensors were fabricated simultaneously by a dc sputtering method and a lift-off process. Thermal annealing of deposited Ti/Pt layers in the temperature range of 300?700 ?C was investigated revealing a strong impact on the Ti/Pt resistivity and, consequently, on the final resistance of fabricated heaters and sensors. Furthermore, it was determined that the temperature coefficient of resistance (TCR) for Ti/Pt temperature sensors and the heater increased with the annealing temperature. Microstructural analysis of deposited and annealed Ti/Pt layers carried out by AES and AFM revealed that recrystallization followed by a grain growth process of heat-treated Ti/Pt layers started at around 500 ?C and correlated well with the behavior of electrical properties, but not with the TCR behavior of annealed layers. To reduce the heat losses of the heated Si platform, the heater and temperature sensors were covered hermetically by anodically bonded Pyrex glass with a prefabricated insulating cavity. According to this approach the power consumption was reduced by more than 25% due to the improved thermal insulation. Additional insulation steps implemented during thermal characterization of the assembled microfluidic platform further reduced the power consumption, but also increased the time response of the microfluidic reactor.

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.

A Strip-Type Microthrottle Pump: Modeling, Design and Fabrication

A novel design for a strip-type microthrottle pump with a rectangular actuator geometry is proposed, with more efficient chip surface consumption compared to existing micropumps with circular actuators. Due to the complex structure and operation of the proposed device, determination of detailed structural parameters is essential. Therefore, we developed an advanced, fully coupled 3D electro-fluid-solid mechanics simulation model in COMSOL that includes fluid inertial effects and a hyperelastic model for PDMS and no-slip boundary condition in fluid-wall interface. Numerical simulation resulted in accurate virtual prototyping of the proposed device only after inclusion of all mentioned effects. Here, we provide analysis of device operation at various frequencies which describes the basic pumping effects, role of excitation amplitude and backpressure and provides optimization of critical design parameters such as optimal position and height of the microthrottles. Micropump prototypes were then fabricated and characterized. Measured characteristics proved expected micropump operation, achieving maximal flow-rate 0.43 mL·min−1 and maximal backpressure 12.4 kPa at 300 V excitation. Good agreement between simulation and measurements on fabricated devices confirmed the correctness of the developed simulation model.

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.

Adaptive Calibration and Quality Control of Smart Sensors

Smart sensors represent an attractive approach in sensor applications due to their adaptability, achieved by means of digital signal processing. Sensor adaptability can be further turned into a major advantage by introduction of smart calibration systems. Smart sensors are generally integrated with signal conditioning circuits. Signal conditioning circuits are needed to adjust the offset voltage and span, for compensation of temperature effects of both offset voltage and span, as well as to provide an appropriately amplified signal. The proposed approach is based on a special case of smart pressure sensors, but the developed calibration system is generally applicable for any kind of smart sensor. In manufacturing of modern electronic devices achieving and maintaining high yield level is a challenging task, depending primarily on the capability of identifying and correcting repetitive failure mechanisms. Yield enhancement is defined as the process of improving the baseline yield for a given technology generation from R&D yield level to mature yield. Yield enhancement is one of the strategic topics of ITRS (International Technology Roadmap for Semiconductors, Test And Test Equipment, 2006). This iterative improvement of yield is based on yield learning process, which is a collection and application of knowledge of manufacturing process in order to improve device yield through the identification and resolution of systematic and random manufacturing events (International Technology Roadmap for Semiconductors, Yield Enhancement, 2006). Yield improvement process will consequentially increase the number of test parameters and hence the calibration system complexity. One of advantages of increasing system complexity is the ability to integrate the input testing processes and output final testing processes into the calibration process itself, thus shortening the total time for calibration. Several types of smart sensors with integrated signal conditioning have been presented over the past few years (Takashima et al., 1997) & (IEEE Std. 1451.2 D3.05, 1997). The calibration processes and temperature compensating methods for these sensors are based either on analog, digital or mixed approaches. Analog approach usually comprises an amplifier with laser trimmable thin film resistors (Chau et al., 1997) & (Wang et al., 2005) or off-chip trimmable potentiometers (Schnatz et al., 1992) & (Lee et al., 1999), to calibrate the sensor span and offset voltage and to compensate for their temperature drift. Analog compensation

In Vivo Experimental Study of Noninvasive Insulin Microinjection through Hollow Si Microneedle Array

An experimental study of in vivo insulin delivery through microinjection by using hollow silicon microneedle array is presented. A case study was carried out on a healthy human subject in vivo to determine the influence of delivery parameters on drug transfer efficiency. As a microinjection device, a hollow microneedle array (13 × 13 mm2) having 100 microneedles (220 µm high, 130 µm-outer diameter and 50 µm-inner diameter) was designed and fabricated using classical microfabrication techniques. The efficiency of the delivery process was first characterized using methylene blue and a saline solution. Based on these results, the transfer efficiency was found to be predominantly limited by the inability of viable epidermis to absorb and allow higher drug transport toward the capillary-rich region. Two types of fast-acting insulin were used to provide evidence of efficient delivery by hollow MNA to a human subject. By performing blood analyses, infusion of more-concentrated insulin (200 IU/mL, international units (IU)) exhibited similar blood glucose level drop (5–7%) compared to insulin of standard concentration (100 IU/mL), however, significant increase of serum insulin (40–50%) with respect to the preinfusion values was determined. This was additionally confirmed by a distinctive increase of insulin to C-peptide ratio as compared to preinfusion ratio. Moreover, we noticed that this route of administration mimics a multiple dose regimen, able to get a “steady state” for insulin plasma concentration.

Impedance Spectroscopy of Suspensions with Paraffin Microcapsules

Impedance spectroscopy of suspensions of paraffin microcapsules with use of the measuring cell with varying distance between the electrodes is presented. The design of a measuring cell is proposed and method for double layer effect elimination is discussed. From colloidal suspension impedance measurements, an electrical model with four classic circuit elements and a constant phase element was evolved. It was found that circuit elements of the proposed electric model correspond to physical properties of suspension.