Design and Modeling of Ferroelectric BST FBARs for Switchable RF Bulk Acoustic Wave Filters.

Multi-standard smartphones have become ubiquitous in everyday life. Such systems operate under different communication standards (2G, 3G, 4G-LTE, WLAN, GPS, Bluetooth, etc.) at different frequencies. Compact and high-performance filters are indispensable for RF front-ends in mobile phones, and RF bulk acoustic wave (BAW) filters, based on piezoelectric film bulk acoustic resonators (FBARs), have become prevalent. Moreover, due to the upcoming Internet of Things (IoT) and 5G, the demand for new technologies that can be employed to design switchable/tunable filters has increased. This dissertation presents one of the new promising technologies, known as intrinsically-switchable BAW filters employing newly-investigated electrostrictive effect in BST thin films. Successful implementation of switchable filters would eliminate/minimize external switches in the design of filter banks, thus leading to significant reduction in their size, cost, and complexity. Contributions of this work are categorized into three major parts. First, the nonlinear circuit modeling procedure for BST FBARs is presented. The nonlinear circuit model, essential for the material characterization and device characterization including linearity analysis, is developed based on the physics of electrostriction-based intrinsically switchable FBARs. Modeling results are in close agreement with dc-bias-voltage and RF-power-level dependent measurement results for BST FBARs. Second, the design methods for BST-on-Si composite FBARs are presented. The designed composite FBAR shows a record Q of 970 at 2.5 GHz among switchable BST resonators. Temperature-dependent characteristics of BST-on-Si composite FBAR devices are also presented with the measured TCF of -35 ppm/K. Furthermore, a raised-frame technique, which has been used to eliminate lateral-wave spurious-modes in piezoelectric BAW resonators, is first employed for switchable ferroelectric FBARs, demonstrating the effectiveness of the frame technique. Finally, the design method for intrinsically switchable BST FBAR filters is presented. The filter design method for ladder-type BAW filters is developed based on image parameters. Closed-form equations are derived for the first time enabling one to accurately design BAW filters. A systematically-designed pi-type BST FBAR filter is fabricated and measured, exhibiting a 1.22% bandwidth at 1.97 GHz with an isolation of greater than 22 dB, having a very small device size of 0.021 mm2.PhDElectrical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/133215/1/seungku_1.pd

Ferroelectric-on-Silicon Switchable Bulk Acoustic Wave Resonators and Filters for RF Applications.

Todays’ multi-band mobile phones’ RF front ends require separate transceivers for each frequency band. Future wireless mobile devices are expected to accommodate a larger number of frequency bands; therefore using the existing transceiver configurations becomes prohibitive. One of the key RF components in wireless devices is the image reject and band-selection filter. Today’s multi-band mobile phones use bulk acoustic wave (BAW) filters in conjunction with solid-state or MEMS-based RF switches for selecting the frequency band of operation. This approach results in very complex circuits. As number of frequency bands increases, ferroelectric BST, operating at its paraelectric phase, has recently been utilized in designing intrinsically switchable BAW resonators and filters due to its voltage induced piezoelectricity. The intrinsically switchable BAW resonators and filters are suitable for designing compact multiband and frequency agile transceivers as they can be switched on and off by simply controlling the dc bias voltage across the ferroelectric layer instead of using separate MEMS or solid-state based RF switches. In this thesis, composite ferroelectric resonators are studied to improve the Q of intrinsically switchable BAW resonators. Intrinsically switchable BAW resonators with record Q values based on ferroelectric-on-silicon composite structures have been demonstrated. In addition, two types of intrinsically switchable BAW filters using ferroelectric-on-silicon composite structure: electrically connected filters and laterally coupled acoustic filters are studied. In the first part of this thesis, the design, fabrication and measurement results for high-Q composite film bulk acoustic resonators (FBARs) are discussed. Subsequently, an intrinsically switchable electrically connected filter based on ferroelectric-on-silicon composite FBARs is presented. Finally, an intrinsically switchable laterally coupled acoustic filter with a ferroelectric-on-silicon composite structure is presented. The reported laterally coupled acoustic filter represents the first demonstration of a BST based intrinsically switchable acoustically coupled filter.PhDElectrical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/107289/1/siss_1.pd

Microelectromechanical Systems for Wireless Radio Front-ends and Integrated Frequency References.

Microelectromechanical systems (MEMS) have great potential in realizing chip-scale integrated devices for energy-efficient analog spectrum processing. This thesis presents the development of a new class of MEMS resonators and filters integrated with CMOS readout circuits for RF front-ends and integrated timing applications. Circuit-level innovations coupled with new device designs allowed for realizing integrated systems with improved performance compared to standalone devices reported in the literature. The thesis is comprised of two major parts. The first part of the thesis is focused on developing integrated MEMS timing devices. Fused silica is explored as a new structural material for fabricating high-Q vibrating micromechanical resonators. A piezoelectric-on-silica MEMS resonator is demonstrated with a high Q of more than 20,000 and good electromechanical coupling. A low phase noise CMOS reference oscillator is implemented using the MEMS resonator as a mechanical frequency reference. Temperature-stable operation of the MEMS oscillator is realized by ovenizing the platform using an integrated heater. In an alternative scheme, the intrinsic temperature sensitivity of MEMS resonators is utilized for temperature sensing, and active compensation for MEMS oscillators is realized by oven-control using a phase-locked loop (PLL). CMOS circuits are implemented for realizing the PLL-based low-power oven-control system. The active compensation technique realizes a MEMS oscillator with an overall frequency drift within +/- 4 ppm across -40 to 70 °C, without the need for calibration. The CMOS PLL circuits for oven-control is demonstrated with near-zero phase noise invasion on the MEMS oscillators. The properties of PLL-based compensation for realizing ultra-stable MEMS frequency references are studied. In the second part of the thesis, RF MEMS devices, including tunable capacitors, high-Q inductors, and ohmic switches, are fabricated using a surface micromachined integrated passive device (IPD) process. Using this process, an integrated ultra-wideband (UWB) filter has been demonstrated, showing low loss and a small form factor. To further address the issue of narrow in-band interferences in UWB communication, a tunable MEMS bandstop filter is integrated with the bandpass filter with more than an octave frequency tuning range. The bandstop filter can be optionally switched off by employing MEMS ohmic switches co-integrated on the same chip.PhDElectrical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/109069/1/zzwu_1.pd