Frances Williams

Ultraviolet radiation sensing in composite oxide semiconductor films

We report on the ultraviolet (UV)-radiation sensing of pulsed-laser deposited In2O3:SnO2:ZnO films grown on glass substrates. The films demonstrate sharp increase (∼0.35 Ω) in electrical resistance on UV illumination. The resistance of the films shows strong spectral (in the vicinity of 325 nm) and power dependence. This is explained due to the presence of defects located at lattice disorders that generate levels within the semiconductor band gap and originate depletion region around them when charged. This reduces the effective conduction region, increasing the effective resistance. These results show new possibilities for the low-cost high performance UV radiation sensors for biosafety.

Acoustic monitoring of electrochemical deposition

In the microelectronics industry, manufacturers are concerned with increasing yield and reducing costs. Monitoring of unit manufacturing processes helps alleviate errors during fabrication, thereby increasing yield and ultimately decreasing cost. This work proposes an acoustic method for in-situ monitoring of electrochemical deposition. A micromachined acoustic sensor was developed for this purpose. During electroplating processes, changes in the plating solution composition result in changes in an acoustic signal transmitted through the bath. A predictive model of the progression of metallization during electroplating was established based on signals from the acoustic sensor. The sensor data and measured plated metal thickness were recorded and mapped to yield an empirical relationship between the two, thereby enabling real-time monitoring of electroplating.

Rectennas performance based on substrates for bio-medical applications

For many sensors, bio-sensors, and probes, it is critical to provide a suitable power source nano or micro scale feature size, flexible structure, and physiologically friendly materials. In this study, rectenna array was considered as a power source using microwave that transmits through the tissues of humans or animals. In addition, biological effects on humans and animals are discussed as well.

Effect of Electrode Pattern on the Actuator Performance of Cellulose Electro-Active Paper

The effect of electrode patterns on the actuator performance of electro-active paper (EAPap) is studied. A rectangular electrode pattern has been typically used for EAPap actuator. Since the electrical field can be concentrated at the edge of electrodes, the electrode patterns of EAPap can influence the actuator performance. Thus, a fishbone pattern electrode was designed and fabricated on EAPap materials and its actuation characteristics were compared with the rectangular electrode ones. Two EAPap materials, DCell, which is made by dissolving cellulose pulp with N,N-Dimethylacetamide and LiCl followed by curing process, and cellophane were used. Bending displacements and the resonance frequencies of EAPap actuators were investigated. Although the bending displacements of the fishbone patterned EAPap actuators were slightly lower than the rectangular patterned actuators, the resonance frequencies of the fishbone patterned actuators were higher than the rectangular patterned actuators. Electrical field concentration around the edge of fishbone pattern electrode might result in increased bending stiffness of the actuator and electrical power consumption. Electrical power consumption and electrode damage of the fishbone pattern electrode were addressed.

Bio/chemical sensors heterogeneously integrated with Si-CMOS circuitry

Sensor arrays for bio/chemical sensing generally incorporate different types of sensors with different substrate coatings, enabling increased sensor sensitivity and selectivity. However, a challenge in using multiple sensor systems is integration with RF electronic circuitry. This work presents the development of flexural plate wave (FPW) acoustic devices implemented in a sensor array and co-integrated on a Si-CMOS circuit. FPWs are highly sensitive to surface perturbations and indirectly sense analytes by detecting mass changes on the sensing plate surface. The sensors are placed in an oscillating circuit, where changes in the oscillation frequency are used to determine changes in the wave velocity due to mass loading by the analyte [1, 2]. Since FPWs are generated in thin plates, these devices are highly sensitive to loading and exhibit the highest mass sensitivities of any acoustic wave device [1, 2]. In the work presented, FPWs are fabricated on Si/SiO2/Si native substrates, with the interdigitated transducers (IDTs) isolated from the active sensing surface. This innovative design enables the sensors to be fabricated and then separated from the native substrate, transferred, and bonded to the host Si-CMOS circuit. Thus, a new approach for the heterogeneous integration of FPW sensors and circuitry is provided. Following integration, the FPWs can be customized with either chemical membranes or biological functionalization. Moreover, this novel approach allows each sensor to be optimized independently before being connected to the host substrate. This paper presents the design, development, and integration process of an FPW sensor on Si-CMOS circuitry.

Study on microwave power via rectenna for airship applications

Flexible dipole rectenna devices offer an attractive source for the delivery of power to high altitude airships, MAVs (Micro-Aero Vehicles), and smart robots. The power converted by the rectenna can vary due to the distance and receiving angle of the source. Regulating the voltage and current delivered to the system will be critical to the proper operation of the remote device. There are various choices for the regulation of the power received and their applicability was explored. Several available regulators were explored in this research. Zener diodes, series pass regulators, three terminal and switching mode regulators were tested to determine which produced the best performance for the application of powering a remote controlled airship. The present research sought to provide stable voltage and current delivered by an array of rectenna.

Design and simulation of PZT-based MEMS piezoelectric sensors

Devices with increased sensitivities are needed for various applications including the detection of chemical and biological agents. This paper presents the design of microelectromechanical systems (MEMS) devices that incorporate lead zirconate titanate (PZT) films in order to realize highly sensitive sensors. In this work, the piezoelectric properties of the PZT are exploited to produce sensors that perform optimally for mass sensing applications. The sensor is designed to operate as a thin-film bulk acoustic resonator (TFBAR) whereas a piezoelectric is sandwiched between electrodes and senses a change in mass by measuring a change in resonance frequency. Modeling of the TFBAR sensor, using finite element analysis software COMSOL, was performed to examine optimal device design parameters and is presented in this paper. The effect of the PZT thickness on device resonance is also presented. The piezoelectric properties of the PZT is based on its crystal structure, therefore, optimization of the PZT film growth parameters is also described in this work. A detailed description of the fabrication process flow developed based on the optimization of the device design and film growth is also given. The TFBAR sensor consists of 150 nm of PZT, 150nm of silicon dioxide, silicon substrate, titanium/platinum bottom electrodes, and aluminum top electrodes. The top electrodes are segmented to increase the sensitivity of the sensor. The resonance frequency of the device is 3.2 GHz.

Growth and properties of PZT -based perovskite multilayers for sensor applications

We have studied ferroelectric properties of Pb (Zr0.6Ti0.4) O3(PZT)/SrTiO3 thin films grown on platinized silicon substrates using pulsed-laser deposition and magnetron sputtering technique. The spontaneous polarization (Ps) and remnant polarization (Pr) varies between 15.5 K and 100 K from 33-38 μC/cm2 and 25-30 μC/cm2,respectively. Similar values of Ps and Pr were also observed until temperature reached to 300K. However, more pronounced ferroelectric hysteresis loops were observed between T= 323 to 353 K. The Ps and Pr remain around 36-40 μC/cm2and 23-28 μC/cm2, respectively, between T = 323 to 353 K. The remnant polarization remains fairly consistent over the chosen temperature range. X-ray diffraction and high-resolution microscopic studies reveal that the Pb (Zr0.6Ti0.4) O3 layers are superior in crystalline quality than that of SrTiO3. The PZT in multilayered films show remarkably enhanced polarization properties relative to their single layers on the same substrates. The collective contribution of dipole moments from each layer is the reason for such enhancement in polarization properties. This growth strategy may be very useful for fabrication of sensitive sensing and other relevant devices.

Design and Fabrication of a Functionally Modified Bimorph Actuator

In recent years, the use of microelectromechanical systems (MEMS) devices has led to high performing actuators for various applications, including unmanned air vehicles (UAVs) for defense applications. The incorporation of MEMS technology in this field has resulted in miniaturized UAVs with the capability of carrying out sophisticated reconnaissance and relaying real time information remotely; however, maneuverability of these devices around obstacles is still a challenge. This paper presents the design and fabrication of a functionally modified bimorph actuator with enhanced UAV aerodynamics and maneuverability. The actuator is a metal-based MEMS device consisting of stainless steel, lead zirconate titanate (PZT), and titanium/platinum electrodes. COMSOL analysis was performed to examine optimal device design parameters and is presented in this paper. The design consists of off-axis PZT segments on a bimorph PZT layer which results in bend twist coupling. A detailed description of the fabrication process flow developed based on the optimization of the device design is also given. MEMS processing technology was incorporated to produce a torsional cantilever beam that produces angular and linear displacement for superior UAV maneuverability and its performance is also presented in this paper.Copyright

Integrating Sensors With Nanostructures for Biomedical Applications

This paper presents the fabrication of sensors that are integrated with nanostructures and bio-functionalized to create novel devices for biomedical applications. Biosensors are in great demand for various applications including for the agriculture and food industries, environmental monitoring, and medical diagnostics. Much research is being focused on the use of nanostructures (nanowires, nanotubes, nanoparticles, etc.) to provide for miniaturization and improved performance of these devices. The use of nanostructures is favorable for such applications since their sizes are closer to that of biological and chemical species and therefore, improve the signal generated. Moreover, their high surface-to-volume ratio results in devices with very high sensitivity. The use of nanotechnology leads to smaller, lower-power smart devices. Thus, this paper presents the integration of sensors with nanostructures for biomedical applications, specifically, glucose sensing. In the work presented, a glucose biosensor and its fabrication process flow are described. The device is based on electrochemical sensing using a working electrode with bio-functionalized zinc oxide (ZnO) nano-rods. Among all metal oxide nanostructures, ZnO nano-materials play a significant role as a sensing element in biosensors due to their properties such as high isoelectric point (IEP), fast electron transfer, non-toxicity, biocompatibility, and chemical stability which are very crucial parameters to achieve high sensitivity. Amperometric enzyme electrodes based on glucose oxidase (GOx) are used due to their stability and high selectivity to glucose. The device also consists of silicon dioxide and titanium layers as well as platinum working and counter electrodes and a silver/silver chloride reference electrode. The chlorination process on the reference electrode was optimized for various times using field emission scanning electron microscope (FESEM) and energy-dispersive X-ray spectroscopy (EDS or EDX) measurements. The ZnO nanorods were grown using the hydrothermal method and will be bio-functionalized with GOx for electrochemical sensing. Once completed, the sensors will be tested to characterize their performance, including their sensitivity and stability.Copyright