Characterization of ZnO/diamond SAW devices elaborated on the smooth nucleation side of MPACVD diamond (original) (raw)
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Freestanding CVD diamond elaborated by pulsed-microwave-plasma for ZnO/diamond SAW devices
Diamond and Related Materials, 2004
In previous work, the feasibility of developing high performance AlNydiamond surface acoustic wave (SAW) devices has been demonstrated using the unpolished nucleation side of freestanding CVD diamond. This process shows the advantage of avoiding the diamond polishing, which is a tedious and a time-consuming technological step. As alternative, we propose the use of a diamond substrate obtained by two stages of growth in pulsed MPACVD to constitute two superposed layers. The first one was deposited at optimal conditions with 2% CH in H gas mixture, leading to a high diamond quality. The second diamond layer is 4 2 used as a support in order to get a freestanding diamond. It has a lower quality because it's obtained by increasing the CH 4 content, thus the growth rate. The first diamond layer combined with piezoelectric film defines the SAW properties. Its thickness is chosen as a function of the acoustic wave penetration depth in order to limit their propagation only in the first diamond layer. Aluminium inter-digital transducers (IDTs) were deposited by conventional contact UV photolithography on the nucleation side of the freestanding diamond. Piezoelectric ZnO film was then deposited by reactive magnetron sputtering to obtain the ZnOyIDT ydiamond structure. Electrical characterization of the SAW device exhibits high filtering properties. The following parameters are obtained with 32 mm wavelength, 3 mm ZnO and 25 mm diamond first layer thickness: acoustic phase velocity: v s9696 mys, w electromechanical coupling coefficient: K s0.75%, temperature coefficient of frequency: TCFs29 ppmy8C. 2
Nanocrystalline ZnO films with strong (0002) texture and fine grains were deposited onto ultra-nanocrystalline diamond (UNCD) layers on silicon using high target utilization sputtering technology. The unique characteristic of this sputtering technique allows room temperature growth of smooth ZnO films with a low roughness and low stress at high growth rates. Surface acoustic wave (SAW) devices were fabricated on ZnO/UNCD structure and exhibited good transmission signals with a low insertion loss and a strong side-lobe suppression for the Rayleigh mode SAW. Based on the optimization of the layered structure of the SAW device, a good performance with a coupling coefficient of 5.2% has been realized, promising for improving the microfluidic efficiency in droplet transportation comparing with that of the ZnO/Si SAW device. An optimized temperature coefficient of frequency of À23.4 ppm 8C À1 was obtained for the SAW devices with the 2.72 mm-thick ZnO and 1.1 mm-thick UNCD film. Significant thermal effect due to the acoustic heating has been redcued which is related to the temperature stability of the ZnO/UNCD SAW device.
AlN/ZnO/diamond structure combining isolated and surface acoustic waves
Applied Physics Letters, 2009
In order to generate surface acoustic waves ͑SAW͒ and waveguiding layer acoustic waves ͑WLAW͒ simultaneously, a multilayer structure of AlN/ZnO/diamond has been proposed. This structure has been investigated theoretically ͑two-dimensional finite element method͒ and experimentally. The nature of the excited modes and their order were identified by modeling and confirmed experimentally by measuring the frequency response of the device in the air and in contact with the liquid. The demonstrated structure can be used to realize a packageless sensor or resonator, using the WLAW alone. A temperature compensated gas or liquid sensor can also be realized by combined usage of the SAW and the WLAW.
Epitaxial ZnO piezoelectric thin films for saw filters
Materials Science in Semiconductor Processing, 1999
ZnO is a wide bandgap semiconductor material with high piezoelectric coupling coecients. It can be used for making low-loss surface acoustic wave (SAW) ®lters operating at high frequency. We report MOCVD growth of epitaxial ZnO thin ®lms on R-plane sapphire substrates. The crystallinity and orientation of the ®lms, as well as the epitaxial relationship between the ZnO ®lms and the R-plane Al 2 O 3 substrate were studied using X-ray diraction techniques. An atomically sharp interface structure was revealed by high-resolution TEM. Surface morphology was investigated using ®eld emission SEM. SAW ®lters with 10 and 16 mm wavelength were fabricated. Low insertion loss and high piezoelectric coupling coecient, up to 6%, were achieved. The acoustic velocities range from 4050 to 5800 m/s, varying as a function of ZnO ®lm thickness. #
High Frequency Surface Acoustic Wave Filter Using ZnO/Diamond/Si Structure
Japanese Journal of Applied Physics, 1994
Diamond films grown by chemical vapor deposition (CVD) method is receiving much attention as surface acoustic wave (SAW) substrate material, due to its remarkable characteristics of large SAW velocity to offer much attraction in fabrication of high frequency SAW devices. The basic properties of SAW propagating in a ZnO/diamond/Si structure were studied utilizing thin film poly-crystalline diamond. Phase velocity, group velocity, electro-mechanical coupling coefficient (K 2), and temperature coefficient of frequency ( TCF) were examined by experiments and theoretical calculations. And it was confirmed that this structure provides high phase velocity up to 10000 m/s, high K 2 up to 4.8% and pratical TCF value of -28 ppm/° C. An 1.3 GHz SAW filter of a ZnO/diamond/Si structure was fabricated for the first time.
Microelectronic Engineering, 2013
Due to its mechanical properties, diamond is very attractive as an active material for the fabrication of SAW resonators for high frequency applications. In this work, the synthesis of piezoelectric AlN films by reactive sputtering at room temperature has been optimized on thick diamond layers grown on Si and alumina substrates in order to process high frequency devices. The effect of diamond underlayer microstructure is evaluated by TEM. Two sets of samples are studied, AlN/NCD/Alumina and AlN/MCD/ Si. The orientation of the AlN grains is shown to improve with the film thickness and the diamond grain size. For NCD underlayer, the AlN deposited on top is more oriented. Moreover, above 1 lm from the AlN/ diamond interface, a high degree of the c-axis orientation (perpendicular to the AlN/diamond interface) is demonstrated even though two different grain lattice orientations are shown to coexist: one with the ð2 1 1 0Þ planes remaining parallel to the TEM-preparation lamella and the other with ð0 1 1 0Þ planes. The AlN/diamond interface is smooth down to the nm-scale.
Applied Physics Letters, 2010
The interdigital transducer ͑IDT͒/ZnO/metal/diamond structure is investigated for use in the design surface acoustic wave ͑SAW͒ devices in the super-high-frequency ͑SHF͒ band. Simulation results indicate that adding a metal buffer layer with a finite thickness significantly increases the coupling coefficient. In the Sezawa mode, the coupling coefficient is 4.71% when an Al interlayer is applied. This coupling coefficient is 75% and 77% larger than those in the IDT/ZnO/diamond and IDT/ZnO/ shorted surface/diamond structures, respectively. The results in this study are useful in designing SAW devices using diamond-based structures with a large coupling coefficient in the SHF band.
—In this work, we report on the fabrication results of surface acoustic wave (SAW) devices operating at frequencies up to 8 GHz. In previous work, we have shown that high acoustic velocities (9 to 12 km/s) are obtained from the layered AlN/diamond structure. The interdigital transducers (IDTs) made of aluminium with resolutions up to 250 nm were successfully patterned on AlN/diamond-layered structures with an adapted technological process. The uniformity and periodicity of IDTs were confirmed by field emission scanning electron mi-croscopy and atomic force microscopy analyses. A highly oriented (002) piezoelectric aluminum nitride thin film was deposited on the nucleation side of the CVD diamond by magnetron sputtering technique. The X-ray diffraction effectuated on the AlN/diamond-layered structure exhibits high intensity peaks related to the (002) AlN and (111) diamond orientations. According to the calculated dispersion curves of velocity and the electromechanical coupling coefficient (K 2), the AlN layer thickness was chosen in order to combine high velocity and high K 2. Experimental data extracted from the fabricated SAW devices match with theoretical values quite well.
Comprehensive characterization of ZnO thin films for surface acoustic wave applications
Journal of Materials Science: Materials in Electronics, 2019
This paper presents a comprehensive characterization of a very smooth, c-axis oriented, highly piezoelectric and electrically resistive 2.5 µm-thick ZnO thin film deposited by a radio frequency (RF) magnetron sputtering system on SiO 2 /Si substrate. Thin film properties such as surface roughness, crystallography, stoichiometry, and electrical resistivity are measured. Twoport surface acoustic wave (SAW) devices with bidirectional interdigital transducer (IDT) periods of 16 µm, 20 µm and 24 µm are fabricated on top of the ZnO thin film. A detailed finite element analysis (FEA) of the thin film is elaborated by varying ZnO thickness and IDT configuration. FEA results shows that acoustic wave velocities and resonance frequencies of the SAW devices are decreasing together with increasing ZnO thickness. Frequency response of the fabricated SAW devices are measured with a vector network analyzer (VNA) and compared to FEA results. First two wave modes, namely the Rayleigh and Sezawa waves, of the fabricated SAW devices on the ZnO thin films are interrogated. Resonance frequencies of the SAW devices with wavelengths of 16 µm, 20 µm, and 24 µm are measured as 204.8 MHz, 176.3 MHz, and 155.3 MHz for the Rayleigh mode, 335.9 MHz, 275.3 MHz, and 235.1 MHz for the Sezawa mode, respectively. In addition, omnidirectional wave propagation of ZnO thin film is shown with 45° rotated IDTs. Overall, experimental results are in good agreement with simulation results, demonstrating ZnO thin film fabrication is successfully carried out, and FEA is an appropriate method for modeling SAW devices on thin films.