Characteristics Analysis of Saw Filter Using Al 0.36 Ga 0.64 N Thin Film
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Characteristics Analysis of Saw Filter Using Al 0.36Ga0.64 N Thin Film
Sun-Ki Kim, Min-Jung Park, Cheol-Yeong Jang, Hyun-Chul Choi, Jung-Hee Lee, and Yong-Hyun Lee School of Electronic Engineering & Computer Science, Kyungpook National University, 1370 Sankyuk-Dong, Buk-Gu, Daegu, Korea, e-mail : [email protected] ABSTRACT AlxGa1-xN sample with x=0.36 was epitaxially grown on sapphire by MOCVD. SAW velocity of 5420 m/s and TCF (temperature coefficient of frequency) of -51.20 ppm/ were measured from the SAW devices fabricated on the AlxGa1-xN sample, and 60 . Electrowhen kh value was 0.078, at temperatures between –30 mechanical coupling coefficient was ranged from 1.26 % to 2.22 %. The fabricated SAW filter have shown a good device performance with insertion loss of -33.853 dB and side lobe attenuation of 20 dB.
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INTRODUCTION
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semiconductors AlN, GaN, and their alloys are important piezoelectric suitable for optoelectric devices as well as blue/green light emitters and surface acoustic wave (SAW) applications [1,2]. Especially AlN is a promising materials for SAW devices because its high SAW velocity which qualifies it for GHz-band applications. Devices working at 2 GHz have already been built [3]. The respective SAW velocities of GaN and AlN are 4800 m/s and 5700 m/s [4]. Theoretical SAW velocity of AlxGa1-xN is therefore expected to be between these values by varying from x = 0 to x = 1, which indicates that the operating frequency of the SAW can be controllable by simply changing Al-mole fraction. EXPERIMENTS The AlxGa1-xN with x=0.36 piezoelectric thin film was grown on sapphire with TMAl flow rate of 40 mol/min, H2/ NH3 substrate using MOCVD at 1035 flow of 4/4 slpm, and growth pressure of 50 torr. Prior to the epitaxial AlxGa1-xN growth, with TMGa flow rate of 30 180 thick GaN initial buffer layer was grown at 550 mol/min. The surface morphology and crystallinity of the AlxGa1-xN thin films were characterized using SEM (scanning electron microscopy) and X-ray rocking curve. To estimate the characteristic parameters, SAW filters with unapodized interdigital transduscer/AlxGa1-xN/sapphire structure were used.
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H3.1.1 Downloaded from https://www.cambridge.org/core. Iowa State University Library, on 08 Jan 2019 at 12:05:48, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1557/PROC-720-H3.1
Figure 1. (a) IDT pattern (b) schematic diagram of the cross-section of fabricated AlxGa1-xN SAW filter.
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The electrode wavelength of the SAW filter was 20, 40, 60 . Al electrodes with thickness of 200 nm were evaporated. The patterning of the electrodes for the SAW IDT was performed by a conventional lift-off process. The respective schematic IDT pattern and the cross-section of the devices are shown in Figure 1 (a) and (b), respectively. The detailed specification is summarized Table . The frequency response of the SAW filters was measured using a HP 8753C network analyzer. SAW velocities were calculated by estimating center fr
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