Ali B. Alamin Dow

Ultrananocrystalline Diamond-Based High-Velocity SAW Device Fabricated by Electron Beam Lithography

Surface acoustic wave (SAW) devices have been used extensively for a variety of applications such as telecommunications, electronic devices, and sensors. The emerging need for high-bit data processing at gigahertz frequencies and the requirement of high-sensitivity sensors demand the development of high-efficiency SAW devices. With the objective of exploiting the high acoustic velocity of diamond, we report on an optimally developed nanodiamond thin film with crystal size of 3-5 nm, embedded in an amorphous carbon matrix with grain boundaries of 1-1.5 nm, that is integrated with aluminum nitride (AlN) to extend the operating frequency of SAW transducers. We utilize this attractive property of diamond through facile synthesis of a bilayer structure consisting of sputtered AlN deposited on an ultrananocrystalline diamond (UNCD) film. We report the realization of a high-frequency SAW resonator, using a device architecture based on an UNCD layer. The UNCD films were synthesized using a microwave plasma-enhanced chemical vapor deposition (MWPECVD) technique and were used to enhance the SAW velocity in the AlN thin film, thus opening the way for the application of CMOS compatible high-frequency SAW devices. The deposition and characterization of UNCD thin films are presented and highlighted for the realization of the SAW resonators. The high velocity associated with the UNCD/AlN bilayered approach together with the high lateral resolution of the interdigital transducers obtained with electron beam lithography is essential for the realization of high-frequency SAW devices. The fabricated devices demonstrate resonance frequencies of 11.3 and 6.2 GHz corresponding to spatial periods of 800 and 1600 nm, respectively, yielding a SAW velocity of 9040 and 10 064 m/s, respectively.

Super-high-frequency SAW transducer utilizing AIN/ultrananocrystalline diamond architectures

SAW devices have been used in a variety of applications including high-volume telecommunications, electronic devices, and advanced sensors. Recently, high-bit-rate data processing in the gigahertz frequency range and ultrahigh-sensitivity sensors have called for the development of advanced SAW transducers. Because of its high acoustic velocity, ultrananocrystalline diamond (UNCD) with a crystal size of 3 to 5 nm, embedded in an amorphous carbon matrix with grain boundaries of 1 to 1.5 nm, is integrated with AlN to extend the operating frequency of SAW devices. We utilize this attractive property of UNCD through the facile synthesis of bilayer architectures consisting of sputtered AlN deposited on UNCD film. The UNCD films were synthesized using microwave plasma-enhanced chemical vapor deposition. The SAW devices were fabricated by electron beam lithography and lift off processes. The fabricated SAW nanodevices exhibit resonance frequencies up to 15.4 GHz. Multiple SAW transducers were fabricated with spatial periods ranging from 580 nm to 3.2 μm.

Harnessing second-order optical nonlinearities at interfaces in multilayer silicon-oxy-nitride waveguides

We demonstrate multi-layer silicon-oxy-nitride (SiON) waveguides as a platform for broadband tunable phase-matching of second-order nonlinear interactions arising at material interfaces. Second-harmonic generation (SHG) is measured with a 2 ps pulsed pump of 1515–1535 nm wavelength, where 6 nW power is generated by an average pump power of 30 mW in a 0.92 mm long device. The wavelength acceptance bandwidth of the SHG is as broad as 20 nm due to the low material dispersion of SiON waveguides. The waveguide structure provides a viable method for utilizing second order nonlinearity for light generation and manipulation in silicon photonic circuits.

Design and Fabrication of a Micropreconcentrator Focuser for Sensitivity Enhancement of Chemical Sensing Systems

The low sensitivity of the gas monitoring system, especially in low concentration range, can be overcome by a miniaturized-based preconcentrator focuser, which can be integrated at the front end of the system. The preconcentrator focuser accumulates, concentrates, and releases the concentrated target analyte upon applying a heating pulse, thus extensively enhancing the sensitivity of the system. Recently, highly strict regulations on the quality of fruits have been applied to deliver high quality fruits to the consumer. Therefore, precise monitoring of ethylene as a ripeness accelerator to the fruits is very important. This paper presents the design, fabrication, and characterization of micropreconcentrator focuser for ethylene monitoring. The device is based on silicon microtrenches that serve as a microheater and microchannels loaded with Carboxen 1000 adsorbents. Thick silicon microtrenches are formed using deep reactive ion etching process. The silicon structures are sandwiched between two Pyrex wafers by anodic bonding. Only clean air is used as a carrier and desorption gas. The enhancement of 100-ppb ethylene concentration is discussed and presented. The device performance for various operations parameters is demonstrated.

Modeling and Analysis of a Micromachined Piezoelectric Energy Harvester Stimulated by Ambient Random Vibrations

Piezoelectric energy microgenerators are devices that continuously generate electricity when they are subjected to varying mechanical strain due to vibrations. They can generate electrical power up to 100 μW which can be used to drive various sensing and actuating MEMS devices. Today, piezoelectric energy harvesters are considered autonomous and reliable energy sources to actuate low power microdevices such as wireless sensor networks, indoor-outdoor monitoring, facility management and biomedical applications. The advantages of piezoelectric energy harvesters including high power density, moderate output power and CMOS compatible fabrication in particular with aluminum nitride (AlN) have fuelled and motivated researchers to develop MEMS based energy harvesters. Recently, the use of AlN as a piezoelectric material has increased fabrication compatibility, enabling the realization of smart integrated systems on chip which include sensors, actuators and energy storage. Piezoelectric MEMS energy microgenerator is used to capture and transform the available ambient mechanical vibrations into usable electric energy via resonant coupling in the thin film piezoelectric material. Analysis and modeling of piezoelectric energy generators are very important aspects for improved performance. Aluminum nitride as the piezoelectric material is sandwiched between two electrodes. The device design includes a silicon cantilever on which the AlN film is deposited and which features a seismic mass at the end of the cantilever. Beam theory and lumped modeling with circuit elements are applied for modeling and analysis of the device operation at various acceleration values. The model shows good agreement with the experimental findings, thus giving confidence in the model.

Analysis of a micromachined piezoelectric energy harvester

Miniaturization is a continuing trend in the electronics industry. The power required by smaller devices has decreased, but the challenge remains to find energy-efficient power sources for them. Battery technology has not been able to keep pace with the extremely rapid developments in microelectronics, drawing attention to energy-harvesting MEMS (microelectromechanical systems) as a viable and clean energy source.1 Autonomous energy harvesters vis-à-vis creating self-powered miniaturized devices is highly sought after in many applications, such as remote supervision of patients’ vital signs and health management, gas and liquid flow control and handling, environmental observation, and security and defense. These demands for miniaturization and autonomy call for the ability to convert mechanical vibrations into electric energy, thus offering batteryfree operation.1, 2 Mechanical energy from vibrating sources in the surrounding environment is pervasive and accessible, found in such places as automobile engines, rotating equipment, and the human body, in all instances translating vibration into electrical energy via the deformation of a piezoelectric material (see Figure 1). Harvesting this energy is one of the most promising transduction techniques owing to the high energy density and ample power it provides (on the order of 100 W). The minimal microfabrication restrictions on such devices, and their amenability to both indoor and outdoor applications, make them useful in a wide range of situations. A piezoelectric energy harvester consists of a piezoelectric film on a silicon cantilever with a seismic mass, sandwiched between electrodes that are used to collect the generated power (see Figure 2). When the piezoelectric material is subjected to mechanical vibrations, stress is induced within the material, thus giving rise to an electromotive force that generates an electrical impulse. We are interested in optimizing the design of Figure 1. Illustration of the piezoelectric (P) transduction technique.

High frequency SAW nanotransducer utilizing ultrananocrystalline diamond/ A1N bimorph architecture

This article reports on the development and realization of a super high frequency surface acoustic wave (SAW) nanotranducer architecture based on a bi-layer of aluminum nitride (AlN) and ultrananocrystalline diamond (UNCD). The SAW nanotransducer was fabricated on an AlN/UNCD structure using electron beam lithography and lift off processes. The SAW device consists of nano inter-digitated transducers (n-IDTs) at both the input and output ports. The fabricated devices exhibited response over a high frequency range, as high as 18.4 GHz, with minimal insertion losses. The good frequency characteristics of the fabricated devices and compatibility with existing fabrication technologies open the way for the realization of advanced AlN/UNCD based transducers.

Stoichiometric amorphous hydrogenated silicon carbide thin film synthesis using DC-saddle plasma enhanced chemical vapour deposition

Silicon carbide is a versatile material amenable to a variety of applications ranging from electrical insulation, surface passivation and diffusion barrier to optical devices. The DC saddle-field plasma enhanced chemical vapour technique is an alternative large area deposition technique. Here we report on the synthesis of stoichiometric hydrogenated amorphous silicon using the dc saddle-field PECVD technique. We also report on the attainment of very smooth surface morphology for the stoichiometric a-SiC:H films in contrast to low carbon content films. Surface roughness of 1 nm rms was demonstrated for films grown at a temperature as low as 225°C.

Design, fabrication and characterization of a micromachined piezoelectric energy harvester excited by ambient vibrations

This research work presents the design, fabrication and characterization of micromachined piezoelectric energy harvester stimulated by ambient random vibrations utilizing AlN as a piezoelectric material. The device design consists of a silicon cantilever beam on which AlN is sandwiched between two electrodes and a silicon seismic mass at the end of the cantilever beam. The generated electric power of the devices was experimentally measured at various acceleration levels. A maximum power of 34 μW was obtained at an acceleration value of 2g for the device which measures 5.6 x 5.6 mm2. Various unpackaged devices were tested and assessed in terms of the generated power and resonant frequency at various acceleration values.

Nanocrystalline diamond/AlN structures for high efficient SAW nano-resonators

Over the last decades, surface acoustic wave (SAW) devices have been involved in a variety of applications including communication systems, physical and chemical sensors and lab on chip. However, increasing demand in high volume communication systems and ultrasensitive sensors has called for advanced SAW devices that can operate at higher frequencies (GHz) while maintaining low insertion levels. Owing to its properties such as very high acoustic velocity, nanocrystalline diamond (NCD) has been utilized for the realization of a high frequency SAW nano-resonators. In this work, we report on the development, fabrication and testing of SAW devices based on aluminum nitride (AlN) and NCD architecture. The NCD films were deposited using microwave plasma enhanced chemical vapour deposition (MWPECVD). The NCD synthesis process details are presented and discussed. An optimized electron beam lithography (EBL) process was used for the realization of high frequency fine resolution SAW nano-resonators on AlN/NCD bi-layer. The fabricated device exhibited a resonance frequency of 11.3 GHz yielding an acoustic velocity of 9040 m/s.