UCLA

The wireless industry has changed our lives in many different aspects in the past decade. As the communication technology develops, the complexity of our mobile RF front-end increases because of advanced communication standards. This requires next generation RF front-end to be more efficient and compact than presently available. Acoustic wave devices have been widely used for filters and diplexers in the radio frequency front-end module due to their excellent quality factor and small footprints at radio frequency. Acoustic duplexers offer great isolation for transmitting and receiving signals at closely spaced frequency bands in frequency division duplex communication systems. However, the exploitation of these acoustic wave technologies remains in the passive domain rather than active domain. This dissertation is to explore parametric mixing and amplification on the acoustic wave platform, with the aim to develop a new class of nonlinear acoustic components such as acoustic mixers providing orders of magnitude improvement in size, and novel acoustic resonators with enhanced and amplified performance. Firstly, the acoustic nonlinear transmission line concept is proposed using the analogy between electromagnetic wave and acoustic wave, i.e., parametric mixing is expected to happen in the nonlinear acoustic waveguide where the mechanical stiffness is modulated by the pump wave. This concept is proved using multi-physics finite element simulation and validated with analytical equations. Secondly, practical implementations of acoustic nonlinear transmission line using nonlinear materials including Barium Strontium Titanite (BST) and Aluminum Nitride (AlN) are investigated. Parametric mixing is observed in the BST coupled surface acoustic wave grating and in the AlN Lamb wave delay line. Comparing to BST implementation, AlN implementation demonstrates a higher nonlinear stiffness modulation under same power level and is more optimal for power efficient parametric mixing and amplification purpose. Lastly, a non-degenerate phase independent parametric Q-enhancement technique is explored and demonstrated on AlN Lamb wave resonators. This technique is implemented by parametrically pumping AlN material stiffness to realize a negative resistance seen at the signal path. A multi-resonance coupled nonlinear model is developed to simulate the parametric coupling of each resonance and extract the nonlinearity of AlN from experimental data. The device quality factor is boosted in both simulation and experiment with proper pump frequency and pump power. This dissertation presents a complete study of parametric mixing and amplification on the nonlinear acoustic platform, and it can be readily capitalized to develop nonlinear acoustic devices for future communication systems.