CAREER:Doped Aluminum Nitride Ferroelectric Microelectromechanical Systems

提案标题：职业生涯：掺杂氮化铝铁电微电子机械系统非技术摘要在移动电话中，压电材料将射频信号转换为机械振动，形成对有效利用射频(RF)频谱至关重要的微型、高选择性前端滤波器。虽然声学滤波技术在现有蜂窝频段中得到了很好的发展，但在已分配用于宽带第五代(5G)蜂窝网络技术的毫米波频段中，用于减轻干扰的微型滤波技术缺乏。拟议的研究将研究将声学前端滤波技术的频率调整到毫米波频段的新方法，而不会出现影响现有频率调整方法的性能下降。拟议研究的成功将使可靠的第五代无线网络更具抗干扰性。这些应用将产生重大的社会影响。技术摘要在扩展声学滤波技术以满足无线通信系统(如第五代(5G)移动网络)的需求时，需要克服两个重大挑战。首先，随着声学谐振器和滤波器的频率扩展到超过6千兆赫(GHz)，尺寸迅速缩小，由于一连串的寄生效应，性能显著下降。这些问题包括由谐振器表面的散射和变薄的金属电极中的阻性损耗引起的谐振器品质因数的退化，以及随着器件电容与与到微小声学器件的芯片布线相关的电容之比的下降而导致的谐振器机电耦合的退化。其次，现有声学谐振器的固定频率操作限制了在布线和开关带来的损耗、面积和成本变得不可行之前可以添加的频段的数量。这项研究旨在研究和开发最近发现的氮化铝钪(AlScN)薄膜的铁电性，以应对这些根本挑战。这项拟议的研究将开发材料沉积技术，允许通过改变Sc掺杂来系统地调整氮化铝钪膜堆的厚度来调整铁电性能。这些技术将被用来形成薄膜堆栈，其中的矫顽场已被设计为随器件厚度而变化，从而允许在可控深度下选择性地反转氮化铝钪薄膜中特定区域的铁电极化。通过薄膜厚度的周期性极化层将被实现，以选择性地激发高阶泛音声学共振，从而实现显著的频率缩放，而不会急剧减小谐振器的尺寸，从而降低先前频率缩放尝试的品质因数和机电耦合。选择性极化技术将被扩展到展示可以在许多倍频程上动态重新配置的声学谐振器。最后，还将探讨与氮化铝钪薄膜性能有关的基本问题，这些问题最终定义了拟议的射频(RF)设备的性能限制。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Proposal Title:CAREER: Doped Aluminum Nitride Ferroelectric Microelectromechanical SystemsNontechnical AbstractIn cellular phones, piezoelectric materials convert radio frequency signals into mechanical vibrations that form the miniature, highly selective, front-end filters critical to efficient utilization of the radio-frequency (RF) spectrum. While acoustic filter technologies are well developed in the existing cellular bands, miniature filtering technologies for mitigating interference are lacking in the Millimeter Wave bands that have been allocated for broadband fifth-generation (5G) cellular network technology. The proposed research will study new methods for scaling the frequency of acoustic front-end filtering technologies to the Millimeter Wave bands without the degradation in performance that plaques existing frequency scaling approaches. Success of the proposed research will enable reliable fifth-generation wireless networks that are more robust to interference. The applications will have major societal impacts.Technical AbstractThere are two grand challenges to overcome in acoustic filter technologies as they are scaled to meet the needs of wireless communication systems, such as fifth-generation (5G) mobile networks. First, as the frequency of acoustic resonators and filters are scaled beyond 6 giga Hertz (GHz), the dimensions rapidly shrink, significantly degrading the performance due to a litany of parasitic effects. These including degradation of the resonator quality factor arising from scattering at the resonator surfaces and from resistive losses in the thinned metal electrodes, and degradation of the resonator electromechanical coupling as the ratio of the device capacitance falls in comparison to the capacitance associated with on-chip routing to the tiny acoustic devices. Second, the fixed frequency operation of existing acoustic resonators limits the number of bands that can be added before the losses, area, and cost introduced by the routing and switches becomes unworkable. This research seeks to study and exploit the recently discovered ferroelectricity in aluminum scandium nitride (AlScN) thin films to address these fundamental challenges. The proposed research will develop material deposition techniques allowing for the systematic tailoring of the ferroelectric properties through the thickness of an aluminum scandium nitride film stack via variations in scandium doping. These techniques will be utilized to form film stacks where the coercive fields have been engineered to vary through the device thickness, allowing for the selective inversion of the ferroelectric polarization of specific regions in the aluminum scandium nitride films at controllable depths. Periodically poled layers through the film thickness will be realized to selectively excite high order overtone acoustic resonances that enable dramatic frequency scaling without the steep reductions in resonator dimensions that degraded both the quality factor and electromechanical coupling of prior frequency scaling attempts. The selective poling techniques will be extended to demonstrate acoustic resonators that can be dynamically reconfigured over many octaves in frequency. Finally, fundamental questions pertaining to the aluminum scandium nitride film properties that ultimately define the performance limits of the proposed radio-frequency (RF) devices will be explored.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.