Atul Vir Singh

Mechanical and structural properties of RF magnetron sputter-deposited silicon carbide films for MEMS applications

In the present work, we report preparation and characterization of silicon carbide (SiC) films obtained by RF magnetron sputtering using a SiC ceramic target. The films were deposited in Ar ambient without external substrate heating. The residual stress of the films was measured as a function of sputtering parameters. The stress of the as-deposited films was observed to be compressive for the entire range of sputtering parameters used in the present work. Postdeposition annealing at 400 ?C in N2?ambient was useful in reducing the stress in the films. On sequentially annealing the films at higher temperatures (600 and 800 ?C), the nature of the stress changed from low compressive to high tensile. A superhard SiC film with low residual compressive stress (58.7 MPa) was obtained with hardness and Youngs modulus values of 49.86 GPa and 363.75 GPa respectively. The x-ray diffraction pattern revealed that the films were either amorphous or nano-crystalline, depending on the deposition parameters and postdeposition annealing temperature. Atomic force microscopy roughness results confirmed good chemical stability of the films in potassium hydroxide and buffered hydrofluoric acid solutions. Several types of micro-structures were fabricated to demonstrate the feasibility and compatibility of these films in MEMS fabrication.

Design and Simulation of a Zinc Oxide Thin Film Bulk Acoustic Resonator Filter for 2.6 GHz Band Applications

ABSTRACT This work presents the design and simulation of a zinc oxide based thin film bulk acoustic resonator (TFBAR) bandpass filter for 2.6 GHz band applications. Third and fifth-order filters in ladder topology are designed and compared. The third-order filter has an insertion loss of 1.62 dB and return loss of 18.97 dB with a bandwidth of 80 MHz whereas the fifth-order filter has insertion loss, return loss, and bandwidth of 2.85 dB, 25.28 dB, and 60 MHz, respectively. With a central frequency of 2.67 GHz, the designed filter has applications in the 2.6 GHz (2500–2690 MHz) band, which has been identified by the International Telecommunication Union as a global frequency band for mobile broadband services.

Preparation and Characterization of Piezoelectric Films of ZnO and AlN by RF Sputtering for RF MEMS Applications

In present work, we report preparation and characterization of piezoelectric films of zinc oxide (ZnO) and aluminum nitride (AlN) by RF magnetron sputtering using respective ceramic targets. The effect of ambient gas, substrate temperature, RF power and sputtering pressure has been studied to get highly c-axis oriented films for potential applications in micro-electromechanical systems. The films were characterized by X-ray diffraction technique to identify the crystallographic orientation. It was observed that the film deposited in pure Argon (Ar) ambient were amorphous or weekly crystallized with no preferred (002) orientation. On the other hand, the films prepared in Ar-O2 for ZnO were highly c-axis oriented. Similarly AlN films were observed to be oriented along c-axis perpendicular to substrate only when deposited in mixture of Ar-N2. To demonstrate the application of piezoelectric properties, an FBAR device (Film Bulk Acoustic Resonator) using ZnO thin film was fabricated. ZnO films are very sensitive to the chemicals used in the micro-electro-mechanical systems (MEMS) fabrication processes which include acids, bases and etchants of different material layers (e.g. SiO2, chromium, gold etc.). A specially designed mechanical jig was used for physically protecting the film during Si anisotropic etching process in potassium hydroxide solution. The potential applications of these films in various RF MEMS devices have been discussed.

Study on Design and Simulation of Zinc Oxide Based Film Bulk Acoustic Resonator for RF Filters

Film Bulk Acoustic Resonator (FBAR) technology is one of the enabling technologies which fulfill the two major needs of wireless industry i.e. high operating frequency range and miniaturization of RF components. This paper presents the design and simulation of a FBAR with zinc oxide as the piezoelectric layer. In the present work, FBAR has been designed and simulated for piezoelectric thickness of 0.75 and 1.25 μm. A thickness of 0.75 μm corresponds to a simulated frequency of 3.57 GHz and can be used for WiMAX applications whereas a 1.25 μm thick layer is suitable for GSM applications at 1.94 GHz. The suitability of the structure for RF filter applications has been observed in terms of electromechanical coupling coefficient.

Design, Fabrication and Characterization of ZnO Based Thin Film Bulk Acoustic Resonators

In the present work we report design, simulation, fabrication and characterization of thin film bulk acoustic resonator (FBAR). The FBAR has been modeled as a single port device with two terminals. The FBAR has been fabricated using Si-SiO2-Al–ZnO-Al structure. Zinc Oxide (ZnO) films were deposited by RF magnetron sputtering using Ceramic ZnO target in Ar-O2 (1:1) ambient without external substrate heating. The XRD result confirms the preferred C-axis orientation of the films required for good piezoelectric properties. These ZnO films have been used to fabricate air gap type resonator. A four mask process sequence was used for this purpose. Lift-off process was used to pattern Al top electrode. In order to create the air cavity under the active device area, the bulk Si was etched in 40 % KOH at 80 °C. A specially designed mechanical jig was used to protect the front side of the device during anisotropic etching. Vector network analyzer was used to measure the reflection coefficient (S11: Return Loss) of the device. The resonant frequency of the resonator was measured to be 2.89 GHz as compare to the simulated frequency of 2.85 GHz with a return loss of 14.51 dB.

Simulation and Analysis of Actuation Voltage of Electrostatically Actuated RF MEMS Cantilever and Fixed – Fixed Switches with Variable Beam Parameters

Radio Frequency (RF) Microelectromechanical system (MEMS) switches are becoming more and more popular in the electronics industry. The main concern in using RF MEMS switch is its high actuation voltage. Thus the main focus in this paper is to obtain low actuation voltage. This paper presents the simulation and analysis of RF MEMS cantilever beam and Fixed – Fixed beam switches. RF MEMS switches simulated in this paper use electrostatic actuation method. Simulations were done using finite element modeling. Different designs and parameters such as gap between electrodes, beam thickness, beam length, and relative permittivity values of medium between electrodes were chosen for analyzing the deflection of beams for various actuation voltages. Perforations of different dimensions were made on both type of beams and the resulted deflections were studied. The simulation results show that the Cantilever and Fixed – Fixed beams follow approximately similar deflection pattern with Cantilever beam deflecting more for applied actuation voltage in all the studies.

Fabrication of Micro-Cantilevers Using RF Magnetron Sputtered Silicon Carbide Films

In the present work, silicon carbide (SiC) films were deposited by RF magnetron sputtering process on Si (100) substrates for micro-cantilever fabrication. The films were deposited without external substrate heating using a ceramic SiC target at 10 mTorr sputtering pressure, 200 W power and 50 mm target-to-substrate spacing. X-ray diffraction pattern shows that the films were amorphous in nature. In order to investigate the chemical inertness, the SiC coated Si substrates were dipped in buffered HF (BHF) at room temperature and in 40% KOH solution at 80 °C for varying length of time. Atomic force microscope was used to investigate surface roughness and morphology of the films before and after chemical processing. Micro-cantilever beams of the SiC film were fabricated by a single mask process. The SiC film was patterned using reactive ion etching (RIE) in SF6-O2 plasma. Thermally evaporated Al film was used as a mask during RIE process. This process also resulted in the formation of convex corners which were exploited for anisotropic etching of Si under the SiC film. The SiC cantilever beams were released by anisotropic etching of Si in KOH at 80 °C without using additional masking material. Scanning electron microscopy was used to observe the fabricated SiC micro-cantilever beams. The morphology of the SiC film after prolonged exposure to KOH was observed to be similar to that of the as-deposited film. The RF magnetron sputtered SiC films were found to be highly inert in KOH and BHF solutions. Due to difficulty in micromachining of bulk SiC material and its high cost, the RF sputtered SiC films on Si can provide a low cost structural material in MEMS.