CAREER:Doped Aluminum Nitride Ferroelectric Microelectromechanical Systems

提案标题：职业生涯：掺杂氮化铝铁电微机电系统非技术摘要在蜂窝电话中，压电材料将射频信号转换成机械振动，形成对射频（RF）频谱的有效利用至关重要的微型、高选择性的前端滤波器。虽然声学滤波器技术在现有的蜂窝频带中得到了很好的发展，但是用于减轻干扰的微型滤波技术在已经被分配用于宽带第五代（5G）蜂窝网络技术的毫米波频带中缺乏。拟议的研究将研究将声学前端滤波技术的频率扩展到毫米波波段的新方法，而不会降低现有频率缩放方法的性能。拟议研究的成功将使可靠的第五代无线网络能够更好地抵御干扰。这些应用将产生重大的社会影响。技术摘要在声学滤波器技术中，当它们被缩放以满足诸如第五代（5G）移动的网络的无线通信系统的需求时，存在两个需要克服的巨大挑战。首先，随着声学谐振器和滤波器的频率被缩放超过6千兆赫兹（GHz），尺寸迅速缩小，由于一连串的寄生效应而显著降低性能。这些包括由谐振器表面处的散射和由变薄的金属电极中的电阻损耗引起的谐振器品质因数的劣化，以及随着器件电容福尔斯与到微小声学器件的片上布线相关联的电容的比率下降而引起的谐振器机电耦合的劣化。第二，现有声学谐振器的固定频率操作限制了在由路由和开关引入的损耗、面积和成本变得不可行之前可以添加的频带的数量。本研究旨在研究和利用最近发现的氮化铝钪（AlScN）薄膜的铁电性，以解决这些根本性的挑战。拟议的研究将开发材料沉积技术，允许通过钪掺杂的变化，通过氮化铝钪膜叠层的厚度的铁电性能的系统定制。这些技术将被用来形成膜堆叠，其中矫顽场已经被设计为通过器件厚度变化，允许在可控深度处的氮化铝钪膜中的特定区域的铁电极化的选择性反转。将实现贯穿膜厚度的周期性极化层，以选择性地激励高阶泛音声学谐振，这使得能够实现显著的频率缩放，而不会急剧减小谐振器尺寸，谐振器尺寸的急剧减小使先前频率缩放尝试的品质因数和机电耦合都劣化。选择性极化技术将被扩展到演示声学谐振器，可以动态地重新配置在许多倍频程的频率。最后，有关氮化铝钪薄膜的性能，最终确定拟议的射频（RF）设备的性能极限的基本问题将explored.This奖项反映了NSF的法定使命，并已被认为是值得通过使用基金会的智力价值和更广泛的影响审查标准进行评估的支持。

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.