Copyright (c) 2009 All rights reserved. http://works.bepress.com/czuo Recent documents in Chengjie Zuo en-us Tue, 17 Nov 2009 23:22:50 PST 3600 http://works.bepress.com/czuo/14 http://works.bepress.com/czuo/14 Mon, 16 Nov 2009 09:51:29 PST Chengjie Zuo Press and News http://works.bepress.com/czuo/13 http://works.bepress.com/czuo/13 Sun, 11 Oct 2009 17:17:34 PDT This work presents the design and demonstration of a microscale inverse acoustic band gap (IABG) structure in aluminum nitride (AlN) with a frequency stop band for bulk acoustic waves in the very high frequency range. Conversely to conventional microscale acoustic band gaps, the IABG is formed by a two-dimensional periodic array of unit cells consisting of a high acoustic velocity material cylinder surrounded by a low acoustic velocity medium. The periodic arrangement of the IABG array induces scattering of incident acoustic waves and generates a stop band, whose center frequency is primarily determined by the lattice constant of the unit cell and whose bandwidth depends on the cylinder radius, the film thickness, and the size of the tethers that support the cylinder. A wide band gap (>13% of the center frequency) is formed by the IABG even when thin AlN films are used. The experimental response of an IABG structure having a unit cell of 8.6 µm and an AlN film thickness of 2 µm confirms the existence of a frequency band gap between 185 MHz and 240 MHz. Nai-Kuei Kuo RF MEMS http://works.bepress.com/czuo/12 http://works.bepress.com/czuo/12 Thu, 23 Jul 2009 07:39:29 PDT This paper presents the first design and demonstration of a novel inverse acoustic band gap (IABG) structure in aluminum nitride (AlN) and its direct integration with piezoelectric contour-mode transducers. The experimental results indicate that the IABG structure has a stop band from 185 MHz to 240 MHz and is centered around 219 MHz with maximum rejection of 30 dB. The ABG-induced phonon scattering causes a frequency band gap that prohibits the propagation of certain acoustic wavelengths. In this work, the IABG unit cell consists of a high acoustic velocity (V) center material, which is formed by 2-μm-thick AlN sandwiched by 200-nm-thick platinum (Pt) and is held by four thin tethers and surrounded by a low acoustic velocity material (air). This cell arrangement enlarges the frequency band gap and eases the requirements on the thickness (d) to lattice constant (a) ratio, which was imposed by previous ABG demonstration in the very high frequency range. The finite element method (FEM) analysis indicates that the IABG can produce a gap-to-midgap ratio of 13.5% even when the d/a ratio is as small as 0.23. This advantage further allows the direct integration of the IABG with high frequency bulk acoustic wave (BAW) transducers. Nai-Kuei Kuo RF MEMS http://works.bepress.com/czuo/11 http://works.bepress.com/czuo/11 Thu, 23 Jul 2009 07:32:15 PDT This paper reports on the demonstration of a new class of ultra-thin (250 nm thick) Super High Frequency (SHF) AlN piezoelectric two-port resonators and filters. A thickness field excitation scheme was employed to excite a higher order contour extensional mode of vibration in an AlN nano plate (250 nm thick) above 3 GHz and synthesize a 1.96 GHz narrow-bandwidth channel-select filter. The devices of this work are able to operate over a frequency range from 1.9 to 3.5 GHz and are employed to synthesize the highest frequency MEMS filter based on electrically self-coupled AlN contour-mode resonators. Very narrow bandwidth (~ 0.35%) and high off-band rejection (~ 35 dB) were achieved at an operating frequency of 1.96 GHz. This first prototype showed insertion loss of 11 dB, which can be improved to few dB if parasitic elements are eliminated or device capacitance is increased. Matteo Rinaldi RF MEMS http://works.bepress.com/czuo/10 http://works.bepress.com/czuo/10 Thu, 23 Jul 2009 07:21:34 PDT This paper reports on the design and experimental verification of a new class of thin-film (250 nm) Super High Frequency (SHF) laterally-vibrating piezoelectric microelectromechanical (MEMS) resonators suitable for the fabrication of narrow-band MEMS filters operating at frequencies above 3 GHz. The device dimensions have been opportunely scaled both in the lateral and vertical dimensions in order to excite a contour-extensional mode of vibration in nano features of an ultra-thin (250 nm) Aluminum Nitride (AlN) film. In this first demonstration two-port resonators vibrating up to 4.5 GHz were fabricated on the same die and attained electromechanical coupling, kt2, in excess of 1.5 %. These devices were employed to synthesize the highest frequency ever reported MEMS filter (3.7 GHz) based on AlN contour-mode resonator (CMR) technology. Matteo Rinaldi RF MEMS http://works.bepress.com/czuo/9 http://works.bepress.com/czuo/9 Thu, 23 Jul 2009 07:12:04 PDT This paper presents the first design and demonstration of a novel inverse acoustic band gap (IABG) structure in aluminum nitride (AlN) and its direct integration with contour-mode wideband transducers in the Very High Frequency (VHF) range. This design implements an efficient approach to co-fabricate in-plane AlN electro-acoustic transducers with bulk acoustic waves (BAWs) IABG arrays (10x10). The IABG unit cell consists of a cylindrical high acoustic velocity (V) media, which is held by four thin tethers, surrounded by a low acoustic velocity matrix (air). The center media is formed by 2-μm-thick AlN, which is sandwiched by 200-nm-thick top and bottom platinum (Pt) layers. The experimental results indicate that the designed IABG has a stop band from 185 MHz to 240 MHz and is centered at 218 MHz in the Γ-Χ direction. This demonstration not only confirms the existence of the frequency band gap in the IABG structure, but also opens possibilities for the integration of ABG structures with RF MEMS devices. Nai-Kuei Kuo RF MEMS http://works.bepress.com/czuo/8 http://works.bepress.com/czuo/8 Thu, 23 Jul 2009 07:03:52 PDT In this paper, we present the first demonstration of the monolithic integration of Aluminum Nitride (AlN) micromechanical contour mode technology filters with dual-beam actuated MEMS AlN switches. This integration has lead to the development of the first prototype of a fully-integrated all-mechanical switchable filter. Integration has been demonstrated by using AlN contour-mode MEMS filters at two center frequencies, i.e. 98.7 and 279.9 MHz. The micromechanical switch design used here is a novel three-finger dual-beam topology that improves the isolation and insertion loss of the switch by decreasing the parasitic coupling between the DC and RF signals over a previous AlN MEMS dual-beam design. With the use of just one switch fabricated right next to, and integrated with the filter, the AlN MEMS filter is effectively turned off and its pass-band transmission is lowered to the out of band level at 279.9 MHz. Nipun Sinha RF MEMS http://works.bepress.com/czuo/7 http://works.bepress.com/czuo/7 Wed, 22 Jul 2009 16:00:06 PDT This paper reports on the first demonstration of a 1.05 GHz microelectromechanical (MEMS) oscillator based on lateral-field-excited (LFE) piezoelectric Aluminum Nitride (AlN) contour-mode resonators. The oscillator shows a phase noise level of -81 dBc/Hz at 1 kHz offset frequency and a phase noise floor of -146 dBc/Hz, which satisfies the GSM requirements of Ultra High Frequency (UHF) local oscillators (LO). The circuit was fabricated in the AMIS 0.5 μm CMOS process, with the oscillator core consuming only 3.5 mW static power. A simple two-mask process was used to fabricate the LFE AlN resonators from 843 MHz to 1.64 GHz with high Q (up to 2,200) and kt2 (up to 1.2%). This process further relaxes manufacturing tolerances and improves yield. All these advantages make it suitable for post-CMOS integrated on-chip direct GHz frequency synthesis in reconfigurable multi-band wireless communications. Chengjie Zuo Analog and RF IC http://works.bepress.com/czuo/6 http://works.bepress.com/czuo/6 Mon, 08 Sep 2008 10:00:42 PDT This paper reports on the first demonstration of multi-frequency (176, 222, 307, and 482 MHz) oscillators based on piezoelectric AlN contour-mode MEMS resonators. All the oscillators show phase noise values between -88 and -68 dBc/Hz at 1 kHz offset and phase noise floors as low as -160 dBc/Hz at 1 MHz offset. The same Pierce circuit design is employed to sustain oscillations at the 4 different frequencies, while the oscillator core consumes at most 10 mW. The AlN resonators are currently wirebonded to the integrated circuit realized in the AMIS 0.5 μm 5 V CMOS process. This work constitutes a substantial step forward towards the demonstration of a single-chip multi-frequency reconfigurable timing solution that could be used in wireless communications and sensing applications. Chengjie Zuo Analog and RF IC http://works.bepress.com/czuo/5 http://works.bepress.com/czuo/5 Mon, 23 Jun 2008 10:54:14 PDT This work reports on piezoelectric Aluminum Nitride (AlN) based dual-beam RF MEMS switches that have been monolithically integrated with AlN contour-mode resonators. The dual-beam switch design presented in this paper intrinsically compensates for the residual stress in the deposited films, requires low actuation voltage (5-20 V), facilitates active pull-off to open the switch and fast switching times (1 to 2 µsec). This work also presents the combined response (cascaded S-parameters) of a resonator and a switch that were co-fabricated on the same substrate. The response shows that the resonator can be effectively turned on and off by the switch. A post-CMOS compatible process was used for fabrication of both the switches and the resonators. The single-chip RF solution presented herein constitutes an unprecedented step forward towards the realization of compact, low loss and integrated multi-frequency RF front-ends. Nipun Sinha RF MEMS