RF Characterization of Mg 0.2 Zn 0.8 O Thin Film Capacitors for MMIC Applications R. Ahmad, M. Salina 1 , S. Sulaiman, A. Awang Teh, M. Kara, M. Rusop 2 and Z. Awang Microwave Technology Centre (MTC), 1, 2 Nano-ElecTronic Centre (NET), Faculty of Electrical Engineering, Universiti Teknologi MARA, Shah Alam, 40450 Selangor, Malaysia imarazak97@yahoo.com, 1 ina1320@yahoo.com, suhana832@salam.uitm.edu, azman.awangteh@gmail.com Abstract— Mg 0.2 Zn 0.8 O thin films are proposed as a new dielectric material for monolithic microwave integrated circuit (MMIC) to replace current dielectric materials due to its high permittivity which can lead to size reduction, in addition to being compatible with semiconductor processing. In this work, Mg 0.2 Zn 0.8 O films were prepared using sol gel spin coating technique, and the films were deposited on Pt-coated Si substrates. Energy dispersive analysis by X-ray (EDAX), scanning (SEM) and field emission scanning electron (FESEM) microscopes were used to study the structural properties. The film thickness was found to be approximately between 0.3 to 0.4 µm with grain sizes about 25 nm. In order to study the radio frequency (RF) properties, capacitors with 50 × 50 μm 2 electrode area were patterned on the MgZnO layer using electron beam lithography (EBL). In this work, we report the RF properties of these films which were measured using Wiltron 37269A vector network analyzer (VNA) and Cascade Microtech on-wafer probes measured over the frequency range of 0.5 to 3 GHz. Our findings show that the films exhibit dielectric constant values between 5 to 55, and loss tangent between 0.02 and 0.04. We feel that our results represent the best RF performance so far by MgZnO films. Keywords- MgZnO, sol-gel, thin films, MMIC capacitors, MMIC dielectrics I. INTRODUCTION Various thin film dielectrics can be used for MMIC applications such as SiO 2 , Si 3 N 4 , polyimide, SrTiO, BST and PZT [1-4]. From the literature, they can be classified into two categories: low and high k dielectrics. Examples of low k dielectrics are SiO 2 (ε r = 4.2), polyimide (5) and Si 3 N 4 (7.5), while high k dielectrics are PZT (where ε r ranges from 400 to1500) and BST (250 to 500). With increasing demands for circuit size reduction in wireless communications low k dielectrics such as SiO 2 and Si 3 N 4 are no longer in favor. Circuits constructed using this material will be relatively large since their sizes are inversely proportional to (ε r ) 1/2 . Therefore materials with higher permittivity are desired for miniaturization [5]. Even though PZT has high dielectric constant, our previous work [4, 6] show that it was difficult to realize 50 Ω lines because the permittivity was too high, this resulted in high return loss. In addition, the films were very lossy and this caused the lines to show very high insertion losses. Thus an alternative dielectric which can offer better high frequency response in terms of moderate dielectric constant and less loss is needed to overcome the aforementioned issues. Besides that, the films should also be compatible with semiconductor processing [7]. Recently, MgZnO thin films have received much attention due to their promising structural and electrical properties such as highly uniform, less crystal defects, transparency in visible region, compatible etching process, high dielectric constant, high resistivity, low temperature growth and tunable bandgap properties [8-10]. Various deposition techniques have been used to prepare Mg x Zn 1-x O films such as molecular beam epitaxy, metal- organic chemical deposition, RF magnetron co-sputtering, pulse laser deposition and sol-gel [11-15]. Among these techniques, the sol-gel process is credited with several advantages including simple, cost effective and the possibility of coating on a large area. In addition, the composition of the films can be altered easily by adjusting different ion proportions in the solution [16]. MgZnO films have been developed by other researchers for several device applications such as thin film transistor, resonator, metal-semiconductor- metal (MSM) solar blind photo-detector and ultraviolet light emitting diode (LED) [17-20]. The films were also reported to be compatible as a seed layer for carbon nanotubes [21, 22]. As reported by J. Liang et al [23], they managed to obtain dielectric constant about 10 at 1 MHz, however the loss tangent were not revealed. In [24], they reported on the fabrication of metal-insulator-silicon (MIS) structures. Capacitor areas of 1.5310 -3 cm 2 were patterned by photolithography with Al as the electrode and the electrical properties were characterized at the said frequency. To the authors’ knowledge, no experimental work on MgZnO was reported to obtain their properties at RF. Thus, it is the purpose of this paper to investigate MgZnO films at high frequencies for potential use in MMIC. In this work, Mg 0.2 Zn 0.8 O was prepared using sol gel technique and deposited on Pt/Si substrate, details of which have been published in [22]. RF test structures which consisted of a combination of a 50 Ω transmission line (TL) and a capacitor was patterned using EBL. The RF properties were obtained and 2011 IEEE International RF and Microwave Conference (RFM 2011), 12th - 14th December 2011, Seremban, Malaysia 978-1-4577-1631-7/$26.00 © 2011 IEEE 420