Development of SAW based gyroscope with high shock and thermal stability

A novel surface acoustic wave (SAW)-based gyroscope with an 80 MHz central frequency was developed on a 128° YX LiNbO₃ piezoelectric substrate. The developed sensor was composed of a SAW resonator, metallic dots, and two SAW delay lines. A SAW resonator was employed to generate a stable standing wave with a large amplitude, metallic dots were used to induce a Coriolis force and to form a secondary SAW, and two delay lines were formed to extract the Coriolis effect by comparing the resonance frequencies between these two delay lines. Coupling of modes (COM) modeling was conducted to determine the optimal device parameters prior to fabrication. According to the simulation results, the device was fabricated and then measured on a rate table. When the device was subjected to an angular rotation, resonant frequency differences between the two oscillators were observed because of the secondary wave, generated by the Coriolis force, perturbed the propagation of the SAW in the sense element. Depending on the angular velocity, the difference of the resonance frequency was linearly modulated. The obtained sensitivity was approximately 172 Hz deg^?1 s^?1 at an angular rate range of 0–500 deg/s. Device performances depending on different mass weights and temperatures were also characterized. Good thermal and shock stabilities were observed during the evaluation process.     

Design of SAW sensor for longitudinal strain measurement with improved sensitivity

This paper presents the design of a highly sensitive surface acoustic wave (SAW)-based sensor with novel structure for the longitudinal strain measurement. The sensor utilizes thin lithium niobate (LiNbO₃) diaphragm as the sensing element rather than the bulk substrate. The application of the diaphragm effectively decreases the cross-sectional area of the strain sensitive element, and meanwhile reduces the resistance between the sensor and the specimen. The newly designed strain sensor is to operate around a frequency of 50 MHz. The insertion loss of − 12 dB and quality factor of 63 are obtained analytically from impulse-response model. The sensor performance with tensile testing of the steel beam is predicted by the finite element method. The prestressed eigenfrequency analysis is conducted with the COMSOL commercial software. The simulation shows the resonance frequency of the sensor shifts linearly with the strain induced in the testing beam. For the SAW sensor with traditional configuration applying 1 mm thick substrate, the strain sensitivity is obtained as 0.41 ppm/με. For the sensor with the novel design employing thin diaphragm with the thickness of 200 μm, the strain sensitivity is increased to 0.83 ppm/με. With the availability of the bulk micromachining of LiNbO₃, the application of the piezoelectric diaphragm as sensing element in SAW strain sensor can be an alternative way to enhance the sensor sensitivity.

     

Nebulization of water/glycerol droplets generated by ZnO/Si surface acoustic wave devices

Efficient nebulization of liquid sessile droplets (water and water/glycerol mixtures) was investigated using standing waves generated using ZnO/Si surface acoustic wave (SAW) devices under different RF powers, frequencies and liquid viscosity (varied glycol concentrations in water). At such high RF powers, there are strong competitions between vertical jetting and nebulization. At lower SAW frequencies of 12.3 and 23.37 MHz, significant capillary waves and large satellite droplets were generated before nebulization could be observed. At frequencies between 23.37 and 37.2 MHz, spreading, displacement or occasionally jetting of the parent sessile droplet was frequently observed before a significant nebulization occurred. When the SAW frequencies were increased from 44.44 to 63.3 MHz, the minimum RF power to initiate droplet nebulization was found to increase significantly, and jetting of the parent droplet before nebulization became significant, although the average size of the nebulized particles and ejected satellite droplets appeared to decrease with an increase in frequency. With the increase of glycerol concentration in the test sessile droplets (or increase in liquid viscosity), nebulization became difficult due to the increased SAW damping rate inside the liquid. Acoustic heating effects were characterized to be insignificant and did not show apparent contributions to the nebulization process due to silicon substrate’s natural effect as an effective heat sink and the employment of a metallic holder beneath the ZnO/Si SAW device substrates.     

基于ZnO/Glass声表面波器件的高速紫外传感特性研究

基于氧化锌/玻璃(ZnO/Glass)结构的声表面波(SAW)器件可以用来制作性能优良的紫外探测器。使用有限元分析软件COMSOL Multiphysics仿真了该种结构的声表面波器件,并得到其S11参数。基于仿真结果,制备了相应的SAW器件,实验所用ZnO薄膜采用直流反应磁控溅射方法沉积,所制备的ZnO薄膜呈(0002)取向。基于该种结构的SAW紫外探测器对紫外光的反应时间仅3 s,其紫外探测的灵敏度高达36.4×10-6/mW/cm2。     

Micro-hotplate based temperature stabilization system for CMOS SAW resonators

Due to the sensitivity of the piezoelectric layer in surface acoustic wave (SAW) resonators to temperature, a method of achieving device stability as a function of temperature is required. This work presents two methods of temperature control for CMOS SAW resonators using embedded polysilicon heaters. The first approach employs the oven control temperature stabilization scheme. Using this approach, the device’s temperature is elevated using on-chip heaters to T_max = 42°C to maintain constant device temperature. Both DC and RF measurements of the heater together with the resonator were conducted. Experimental results have indicated that the TCF of the CMOS SAW resonator of −97.2 ppm/°C has been reduced to −23.19 ppm/°C when heated to 42°C. The second scheme uses a feedback control circuit to switch the on-chip heaters on and off depending on the ambient temperature. This method provided reduction of the TCF from −165.38 ppm/°C, to −93.33 ppm/°C. Comparison of both methods was also provided.     

Simulations,fabrication, and characterization of d31 mode piezoelectric vibration energy harvester

This paper presents the development work on d₃₁ mode piezoelectric vibration energy harvester. The device structure consists of a fixed-free type cantilever beam with a seismic mass attached at the free end of the beam. On top of the cantilever beam, a ZnO piezoelectric layer is sandwiched between two metal electrodes. The harvester is designed using an FEM tool CoventorWare. The simulations are carried out to estimate the resonance frequency, mises stress, optimal load resistance, and generated power. The optimized design is then implemented using a five mask SOI bulk micromachining process. The fabricated harvester is characterized for frequency response using Polytec MSA-500 Micro System Analyzer. The experimental resonance frequency is found to be 235.38 Hz. The harvester is also evaluated for generated open-circuit voltage when subjected to harmonic acceleration. The open-circuit peak-to-peak voltage for 0.1 g acceleration is found to be 306 mV.

     

Enhancement of microfluidic efficiency with nanocrystalline diamond interlayer in the ZnO-based surface acoustic wave device

Ultra-smooth nanocrystalline diamond (UNCD) films with high-acoustic wave velocity were introduced into ZnO-based surface acoustic wave (SAW) devices to enhance their microfluidic efficiency by reducing the acoustic energy dissipation into the silicon substrate and improving the acoustic properties of the SAW devices. Microfluidic efficiency of the ZnO-based SAW devices with and without UNCD inter layers was investigated and compared. Results showed that the pumping velocities increase with the input power and those of the ZnO/UNCD/Si devices are much larger than those of the ZnO/Si devices at the same power. The jetting efficiency of the droplet was improved by introducing the UNCD interlayer into the ZnO/Si SAW device. Improvement in the microfluidic efficiency is mainly attributed to the diamond layer, which restrains the acoustic wave to propagate in the top layer rather than dissipating into the substrate.     

A single ZnO tetrapod-based sensor

Transferable ZnO tetrapods were grown by an aqueous solution method. An individual ZnO tetrapod-based sensor was fabricated by in situ lift-out technique and its ultraviolet (UV) and gas sensing properties were investigated. This single tetrapod-based device responds to the UV light rapidly and showed a recovery time of about 23 s. The sensitivity of a single ZnO tetrapod sensor to oxygen concentration was also investigated. We found that when UV illumination is switched off, the oxygen chemisorption process will dominate and assists photoconductivity relaxation. Thus relaxation dynamics is strongly affected by the ambient O₂ partial pressure as described.We also studied the response of ZnO tetrapod-based sensor in various gas environments, such as 100 ppm H₂, CO, i-butane, CH₄, CO₂, and SO₂ at room temperature. It is noted that ZnO tetrapod sensor is much more sensitive to H₂, i-butane and CO. It is demonstrated that a ZnO tetrapod exposed to both UV light and hydrogen can provide a unique integrated multiterminal architecture for novel electronic device configurations.     

Simulation,mathematical modeling,fabrication and experimental analysis of piezoelectric acoustic sensor for energy harvesting applications

In this paper, an acoustic sensor having ZnO based circular diaphragm sandwiched between two aluminum electrodes as the key element that can find applications in energy harvesting from acoustic sources has been designed, modeled, simulated, fabricated and tested. The ZnO layer is RF sputtered on Silicon substrate and a cavity has been formed by back etching the substrate. The dimensions of the structure are chosen such that the natural frequency of the structure closely matches with that of source frequency to get maximum output voltage due to resonance. The structure is mathematically modeled by Lumped Element Model method and simulated with Finite Element Model method. The experimental results indicate approximately 40 mV output voltage (Open circuit) at 140 db and the natural frequency in the range 11–12 kHz which is in close approximation with the results in mathematical model and simulated structure.

     

Fabrication of the cyclical fluid channel using the surface acoustic wave actuator and continuous fluid pumping in the cyclical fluid channel

A surface acoustic wave (SAW) device has been reported as a micro fluid device such as a pump of a water droplet so far (Renaudin et al. in μTAS, pp 599–601, 2004, 1:551–553, 2005; Sritharan et al. in Appl Phys Lett 88:054102, 2006; Wixforth in Anal Bioanal Chem 379:982–991, 2004; Yamamoto et al. in μTAS, pp 1072–1074, 2005). The SAW device is an interdigital transducer (IDT) fabricated on the piezoelectric substrate only. IDTs are advantageous in terms of integration, miniaturization, free position setting on the substrate and simple fabrication process because of their simple structure. Therefore, the SAW device is easy to apply to integrated chemical system such as lab-on-a-chip. The SAW drives the liquid homogenously by the transmission of surface vibrations of the substrate. Thus, both ends of the channel for pressure loading are not necessary to pump the liquid by using the SAW. The SAW can pump the liquid in both of a closed channel and an opened channel, although continuous flow pumping using an external pump is difficult for no loading pressure in the closed fluid channel. In this paper, we proposed and fabricated the micro fluid devices combined cyclical fluid channel and SAW actuator for liquid pumping. This device is fabricated on a piezoelectric substrate (LiNbO₃) with UV photolithography and wet etching. Structure material of cyclical fluid channel is epoxy photoresist SU-8 100. Then, it is demonstrated to continuous flow pumping and reciprocal flow pumping in the channel. As a result of optimization of a SAW pump’s structural parameter, 32.5, 71.3 and 108.0 mm/s are achieved in the 500, 1,000 and 2,000 μm channel width as a maximum flow velocity.     

Study and design of resistive switching behaviors in PMMA-based conducting-bridge random-access memory (CBRAM) devices

The fabrication and the performance of PMMA resistive switching device have been studied by using FR-4 (copper), PMMA (poly methyl methacrylate) and aluminum as the active anode, the solid electrolyte and the inert cathode respectively. By etching the copper surface with the acid solution [4HNO₃ + 11H₃PO₄ (98 %) + 5CH₃COOH] at 60 °C for 2 min, a good performance of Cu/PMMA/Al device, which can switch until 2300 cycles, has been realized. The spin rate for forming the PMMA coating plays a decisive role in the performance of Cu/PMMA/Al device. The best performance of the Cu/PMMA/Al device was obtained only when the spin rate of deposition of PMMA reached 4000 rpm (low thickness).

     

A vertical structure photodetector based on all‐inorganic perovskite quantum dots

In this work, the vertical structure photodetector based on CsPbBr₃ quantum dots (QDs) with a structure of indium tin oxide (ITO)/zinc oxide (ZnO)/CsPbBr₃ QDs/Au is reported. In this device, CsPbBr₃ QDs film works as the light‐harvesting layer, and ZnO QDs film acts as the electron transport channel, which can extract the electron efficiently and improve the quality of CsPbBr₃ QDs film. As a result, the on/off ratio, detectivity and rise time (decay time) of CsPbBr₃/ZnO hybrid photodetector are measured to be 2.4 × 10⁶, 2.25 × 10¹¹, and 62 milliseconds (82 ms) under 0‐V bias. This work inspires the development of vertical structure photodetectors based on the all‐inorganic perovskite QDs.     

Microfabricated centrifugal pump driven by an integrated synchronous micromotor

This paper presents the development of a new design of the microfabricated centrifugal force pump. The pumping concept is based on running an impeller (a rotor including permanent magnets carrying straight and backward blades) within an integrated synchronous motor, which can be operated at different rotational speeds to pump water. The impeller is 5.5 mm in diameter, and is 1.5 mm in height. This micropump with 7-straight-blade impeller can operate smoothly up to a rotational speed of 9000 rpm. It can deliver a non-pulsating maximum flow rate of up to 12 ml/min and allows water to be pumped up to a 24 cm water head. Additionally, the micropump with the backward-blade-impeller pump delivered a flow rate of up to 14.3 ml/min. at a rotational speed of 11,400 rpm with no back pressure. The micropump was patterned using a series of microfabrication processes including sputtering, photolithography and electroplating within a clean room. Such a pump can be integrated into a system of a compact size and can provide a wide range of flow rates. It could also be a promising device for use within biological and micro biomedical fields. To our knowledge, this is the smallest centrifugal pump in the world with an integrated electromagnetic synchronous motor that offers such high flow rates.

     

Development of temperature-control system for liquid droplet using surface Acoustic wave devices

In this paper, we present a liquid-droplet-heating system using a surface acoustic wave (SAW) device. When liquid is placed on a Rayleigh-SAW-propagating surface, a longitudinal wave is radiated into the liquid. If the SAW amplitude increases, the liquid shows non-linear dynamics, such as vibrating, streaming, small droplet flying, and atomizing. This phenomenon is well known as SAW streaming. The liquid temperature is measured during the longitudinal wave radiation and found to increase. First, the mechanism of the liquid-heating effect is discussed on the basis of experimental results. The surface electrical condition is changed to investigate the effect of dielectric heating. The obtained results indicate that the radiated longitudinal wave causes liquid heating and the dielectric heating effect does not. Second, the fundamental properties of the liquid temperature are measured by varying the applied voltage, duty factor, and liquid viscosity. The liquid temperature is found to be proportional to the duty factor and the square of the applied voltage. Therefore, the liquid temperature can be controlled by these applied signals. Also, by using highly viscous solutions, the liquid temperature is increased to more than 100 °C. Moreover, for chemical applications, the possibility of periodic temperature control is tested by varying the duty factor. The obtained results strongly suggest that an efficient thermal cycler is realized. A novel application of the SAW device is proposed on the basis of SAW streaming.     

Highly sensitive mass sensor using film bulk acoustic resonator

Film bulk acoustic resonators (FBAR) have recently been adopted as alternatives to surface acoustic wave (SAW) in high frequency devices, due to their inherent advantages, such as low insertion loss, high power handling capability and small size. FBAR device can also be one of the standard components as mass sensor applications. FBAR sensors have high sensitivity, good linearity, low hysteresis and wide adaptability. In this study, a highly sensitive mass sensor using film bulk acoustic resonator was developed. The device structure of FBAR is simulated and designed by the Mason model, and fabricated using micro electromechanical systems (MEMS) processes. The fabricated FBAR sensor exhibits a resonant frequency of 2442.188 MHz, measured using an HP8720 network analyzer and a CASCADE probe station. Experimental results indicate that the mass loading effects agree with the simulated ones. Results of this study demonstrate that the sensitivity of the device can be achieved as high as 3654 Hz cm²/ng.     

Thin polymer film based rapid surface acoustic wave humidity sensors

Polyvinyl alcohol (PVA) and polyvinyl pyrrolidone (PVP) thin films, deposited on the surface of glass slides, were studied using transmission FTIR spectroscopy upon varying relative humidity (RH) from 2 to 70%. The obtained data revealed fast dynamics of water vapor adsorption-desorption with responses on the order of several seconds. Based on the fast FTIR signal intensity changes versus RH, it was proposed that a similar rapid response can be achieved for PVA and PVP coated SAW devices due to changes in mass-loading and film viscoelastic properties upon absorption of water vapor in the films. Sub-micron thickness films were spin-coated onto the surface of LiNbO₃ SAW substrates. Both PVA and PVP based humidity sensors revealed prompt reversible response to variations in humidity, although PVP-based device demonstrated better sensor parameters with total insertion loss variation of about 50 dB over the studied RH range and response time 1.5 s for the humidity step 5-95% (recovery time - 2.5 s), representing one of the fastest SAW-based humidity sensors reported to date.     

Fabrication of microfluidic devices for packaging CMOS MEMS impedance sensors

This work presents a polydimethylsiloxane (PDMS) microfluidic device for packaging CMOS MEMS impedance sensors. The wrinkle electrodes are fabricated on PDMS substrates to ensure a connection between the pads of the sensor and the impedance instrument. The PDMS device can tolerate an injection speed of 27.12 ml/h supplied by a pump. The corresponding pressure is 643.35 Pa. The bonding strength of the device is 32.44 g/mm². In order to demonstrate the feasibility of the device, the short circuit test and impedance measurements for air, de-ionized water, phosphate buffered saline (PBS) at four concentrations (1, 2 × 10⁻⁴, 1 × 10⁻⁴, and 6.7 × 10⁻⁵ M) were performed. The experimental results show that the developed device integrated with a sensor can differentiate various samples.     

Effect of dispersed phase viscosity on maximum droplet generation frequency in microchannel emulsification using asymmetric straight-through channels

Uniformly sized droplets of soybean oil, MCT (medium-chain fatty acid triglyceride) oil and n-tetradecane with a Sauter mean diameter of d _3,2 = 26–35 μm and a distribution span of 0.21–0.25 have been produced at high throughputs using a 24 × 24 mm silicon microchannel plate consisting of 23,348 asymmetric channels fabricated by photolithography and deep reactive ion etching. Each channel consisted of a 10-μm diameter straight-through micro-hole with a length of 70 μm and a 50 × 10 μm micro-slot with a depth of 30 μm at the outlet of each channel. The maximum dispersed phase flux for monodisperse emulsion generation increased with decreasing dispersed phase viscosity and ranged from over 120 L m⁻² h⁻¹ for soybean oil to 2,700 L m⁻² h⁻¹ for n-tetradecane. The droplet generation frequency showed significant channel to channel variations and increased with decreasing viscosity of the dispersed phase. For n-tetradecane, the maximum mean droplet generation frequency was 250 Hz per single active channel, corresponding to the overall throughput in the device of 3.2 million droplets per second. The proportion of active channels at high throughputs approached 100% for soybean oil and MCT oil, and 50% for n-tetradecane. The agreement between the experimental and CFD (Computational Fluid Dynamics) results was excellent for soybean oil and the poorest for n-tetradecane.     

CMOS-MEMS resonant pressure sensors: optimization and validation through comparative analysis

An optimized CMOS-MEMS resonant pressure sensor with enhanced sensitivity at atmospheric pressure has been reported in this paper. The presented work reports modeling and characterization of a resonant pressure sensor, based on the variation of the quality factor with pressure. The relevant regimes of air flow have been determined by the Knudsen number, which is the ratio of the mean free path of the gas molecule to the characteristic length of the device. The sensitivity has been monitored for the resonator design from low vacuum to atmospheric levels of air pressure. This has been accomplished by reducing the characteristic length and optimization of other parameters for the device. While the existing analytical model has been adapted to simulate the squeeze film damping effectively and it is validated at higher values of air pressure, it fails to compute the structural damping mechanisms dominant in the molecular flow regime, i.e. at lower levels of air pressure. This discrepancy has been solved by finite element modeling that has incorporated both structural and film damping effects. The sensor has been designed with an optimal geometry of 140 × 140 × 8 µm having 6 × 6 perforations along the row and column of the plate, respectively, for maximum Q, with an effective mass of 0.4 µg. An enhanced quality factor of 60 and reduced damping coefficient of 4.34 µNs/m have been obtained for the reported device at atmospheric pressure. The sensitivity of the manufactured device is approximately −0.09 at atmospheric pressure and increases to −0.3 at 40 kPa i.e. in the lower pressures of slip flow regime. The experimental measurements of the manufactured resonant pressure sensor have been compared with that of the analytical and finite element modeling to validate the optimization procedure. The device has been manufactured using standard 250 nm CMOS technology followed by an in-house BEOL metal-layer release through wet etching.

     

Energy-less respiration monitoring device using thermo-sensitive film

We propose an easy-to-use energy-less respiration monitoring device for monitoring the breathing flow using a thermo-sensitive film. Thermo-sensitive film less than 0.01 mm thick with thermo-sensitive ink and a base film were wrapped over the aperture and partially produced in the tube for monitoring the breathing status. The aperture used as the respiration monitoring area, also worked as thermal isolation to shorten the response time and to decrease thermal capacity in the monitoring area. The response time was investigated using a response evaluation device (designed and produced using MEMS technology) to follow the temperature change with the breathing cycle of 0.3 Hz. The response time depended on the thickness of both the ink and the base film and decreased with the decrease of the thickness due to thermal capacity reduction. The obtained minimum response time was 373 ms when the ink thickness was 6.8 μm and the base film thickness was less than 5.0 μm. The color of the ink at the breathing monitoring area formed on the aperture successfully changed from blue to transparent according to the temperature change of the airflow.