Roy Paily Palathinkal

Mass Loading in Coupled Resonators Consisting of SU-8 Micropillars Fabricated Over SAW Devices

Surface acoustic wave (SAW) sensors extensively employ mass loading effect of a sensing film coated over the surface of a SAW device. We report experimental and simulation results of mass loading by SU-8 micropillars (in place of sensing film) attached normal to the surface of SAW resonators. For certain size of micropillars, we have observed an increase in the resonance frequency of the resonator, in contrast to the decrease in the resonance frequency normally caused by mass loading. The SAW resonator and the pillars constitute a system of coupled resonators, and for high values of stiffness at the interface of the pillar and substrate the shift in the resonance frequency is positive.

HUMIDITY SENSOR USING NIPAAm NANOGEL AS SENSING MEDIUM IN SAW DEVICES

In this paper we report poly N-isopropylacrylamide (NIPAAm) nanogel used as sensing medium in Rayleigh wave type surface acoustic wave (SAW) devices to measure relative humidity. NIPAAm is synthesized by single-step surfactant-free emulsion polymerization reaction method. The prepared nanogel particles have dimensions less than 180 nm. Dynamic light scattering (DLS) analysis of these particles shows increase in size of the particles up to 100% when dispersed in water at room temperature. In this work we have developed two types of relative humidity (RH) sensors. In the first type commercial SAW resonators with resonance frequency at 315 MHz from EPCOSTM were used in our experiment. The casings of two resonators were removed carefully and one of them was left as such to serve as the reference device. The other was coated with the NIPAAm nanogel and used as the sensor. In the second type of SAW-based humidity sensor aluminum interdigital transducers (IDT) are fabricated over YZ lithium niobate piezoelectric substrate using metallization and lithography techniques. The fabricated IDTs have the pitch length of 34 μm and a resonance frequency of 51.6 MHz. Response of sensor to RH is measured by measuring the scattering parameters of both the types of sensors and reference devices recorded using the network analyzer.

Investigation on Resonance Effects of Closely Resonating Nano-Pillars Attached to SAW Resonator

Surface acoustic wave (SAW) sensors form an important class of micro sensors in the microelecto mechanical systems (MEMS) family. Mass loading effect of a sensing medium is one of the prime sensing principles in SAW sensors. Recently we reported mass loading effect of high aspect ratio nano-pillars attached to a SAW resonator. We observed increase in resonance frequency of the SAW resonator in addition to the general mass loading characteristics. We concluded that when the resonance frequency of the pillar is equal to the SAW resonator frequency, the resonance frequency shift caused by mass loading of pillar tends to a negligible value. When such resonating pillars are used as sensing medium in SAW sensors, even a very small change in the dimension of the pillar will offer significant resonance frequency shift. Accordingly, high sensitive SAW sensors can be developed. However in practice it’s quite difficult to manufacture nano-pillars with accurate dimensions such that they resonate with SAW resonator. There is more probability that the pillars may closely resonate with SAW device and offer mass loading. In the present work we have extended our earlier work and performed finite element method (FEM) simulation to study the insight physics of the closely resonating pillars and their effects on acoustic wave propagating on SAW substrate. In this paper we present the discussion on the resonance effects of typical closely resonating pillars on resonance frequency spectrum of the SAW resonator and observations in the pressure wave at the contact surface of the pillar and SAW resonator substrate. It is observed that when the nano-pillars closely resonate with SAW resonator, the pillar oscillations combine with waves propagating in the substrate and introduce beat frequencies. The results and discussion of this paper adds additional information in designing SAW based coupled resonating systems.

Implementation of the MPS in Voltage Controlled Oscillator

Voltage controlled oscillators are used in many analog and RF signal processing systems. It is one of the key building blocks of RF transceivers. With the rapid growth and advancement of wireless communication systems and standards, there has been an increasing demand of high performance and fully integrated GHz voltage controlled oscillators.

Multilayer Pyramidal Symmetric Inductor

In most of the integrated circuits like amplifiers, mixers, oscillators, etc., the differential topology is preferred because of its less sensitivity to noise and interference. There are mainly two categories of differential inductor design found in the literature. The first one is a pair of asymmetric planar inductors connected together in series [1] as shown in Fig. 1.9 symmetric (differential). Since the currents always flow in opposite direction in these two inductors, there must be enough spacing between them to minimize electromagnetic coupling. As a result, the overall area occupied is very large. The second one is the planar symmetric inductor of [2] as shown in Fig. 1.10 which is realized by joining coupled microstrip from one side of an axis of symmetry to the other using a number of cross-over and cross-under connections. An intermediate metal layer is dedicated for the underpass of the cross coupled connections. The center-tapped idea was proposed in [3] for balanced circuits and this type of winding of the metal trace was first applied to monolithic transformers [4]. The symmetrical inductor under differential excitation results in a higher quality factor and self resonance frequency. It also occupies less area than its equivalent pair of asymmetrical inductors. Since these structures are planar, the area is still large. Minimization of inductor area is equally important as enhancing the performance to reduce the production cost. A multilevel symmetric inductor can be realized by stacking two differential inductor of [2] as shown in Fig. 3.1. The structure is a natural extension of the planar differential inductor. This structure is referred hereafter as multilayer conventional symmetric inductor. Realization of cost effective symmetric inductor structures with minimum area without performance degradation is addressed in this chapter.

Optimization of Spiral Inductor with Bounding of Layout Parameters

A typical spiral inductor design problem is to determine its optimum layout parameters for a given inductance that will result in the highest quality factor at desired frequency. This chapter discusses a new approach for spiral inductor design and its optimization.

Fabrication of High Aspect Ratio SU-8 Microstructures on Piezoelectric Transducers

A methodology to fabricate high aspect ratio (HAR) SU-8 micro structures on piezoelectric and metallic substrates is presented. In this work, several fabrication trials were carried out to optimize the SU-8 fabrication process. The fabrication recipe mentioned in the SU-8 (Microchem, USA) datasheet is employed for the initial fabrication trials. The SU-8 structures (micropillars) fabricated during these trials resulted in poor bonding with the surface of piezoelectric substrate. In the later trials a thin film of OmniCoat (Microchem, USA) is coated over the substrate before coating the SU-8 film to improve the adhesion quality of the SU-8 micropillars to the substrate. The fabrication methodology used during the trails and results on the quality of the fabricated HAR SU-8 pillars are discussed in the paper.

Performance Comparison of Interdigitated Thin-Film Field-Effect Transistors Using Different Purity Semiconducting Carbon Nanotubes

In this paper, we present the fabrication and characterization of semiconducting carbon nanotube thin-film field-effect transistors (SN-TFTs). High-k dielectric material, hafnium-oxide (HfOX) is used as the gate-oxide of the device. A Thin-film of semi-conducting single walled carbon nanotube (SWCNT) is deposited on the amino-silane modified HfOX surface. Two types of SN-TFTs with interdigitated source and drain contacts are fabricated using 90% and 95% purity of semiconducting SWCNTs (s-SWCNT), have exhibited a p-type behavior with a distinct linear and saturation region of operation. For 20 µm channel length SN-TFT with 95% pure s-SWCNTs has a peak on-off current ratio of 3.5×104 and exhibited a transconductance of 950 µS. The SN-TFT fabricated with HfOX gate oxide has shown a steep sub-threshold slope of 750 mV/decade and threshold voltage of -0.7 V. The SN-TFT of channel length 50 µm has exhibited a maximum mobility of 26.9 cm2/V•s.