Ultra-Low Noise Mechanical Frequency-Divided MEMS-Based Oscillator

该研究项目旨在利用微型机械的新功能，使便携式个人雷达具有与要求苛刻的平台（如飞机、船只和跟踪系统）上使用的大型雷达相当的分辨率。在这里，由于任何雷达的分辨率在很大程度上取决于其询问信号的稳定性，因此产生该信号的内部振荡器的质量是雷达性能的最重要决定因素之一。正是出于这个原因，最强大的雷达使用基于“波塞冬”振荡器的频率信号发生器，这种振荡器的稳定性来自体积庞大（且昂贵）的蓝宝石负载腔谐振器。然而，这种方法的大小和成本限制了它在大型不可移植应用程序中的使用。本文的研究打破了这种模式，认识到一个振荡器参考了由钻石材料构成的微小机械谐振结构的集合，可以潜在地与波塞冬振荡器相媲美，甚至可能超过波塞冬振荡器，所有这些都是在一个小得多的形状因素。事实上，小到足以支持高分辨率个人雷达的尺寸可能触手可及，这可能会使一系列新的个人功能成为可能，包括测距、远程定位服务和局部区域传感，以识别机会，例如，当一个人走过它们时，有趣的商品的销售、最喜欢的食物等。该研究特别探索了使用微机械谐振器和低于20纳米的电极-谐振器间隙的参数机械频率划分，这些间隙共同推动了振荡器的短期稳定性和性能指标向最佳雷达振荡器的方向发展，但尺寸要小得多。在这里，由于纳米制造技术的进步，微小的电极到谐振器的间隙增加了电容间隙转导微机械谐振器的机电耦合，使其能够支持千兆赫振荡器，同时保持其创纪录的质量因素，这两者都降低了相位噪声和功耗。20纳米以下的间隙还允许更宽的频率调谐，以及在更高的共振频率下使用参数激励，这反过来又使机械方法能够通过分频和近载波滤波的组合进一步降低相位噪声，所有这些都几乎没有功率损失。虽然减少间隙可以实现前所未有的微机械谐振器和振荡器性能，但它也阐明了在纳米尺度上更明显地表现出的基本物理限制，包括非线性噪声倍增、不适当的注入锁定、卡西米尔力、增强的（不必要的）加速度灵敏度，以及对有限制造公差和应力的弹性较差。虽然这些生理上的限制可能对表现有害，但却为科学研究开辟了肥沃的土壤。事实上，通过建模非线性对振荡器限制和相位噪声的影响所获得的经验教训可能是推动微机械振荡器进入上述高端应用的关键。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

This research program aims to harness new capabilities in miniature mechanics that enable portable personal radar with resolution commensurate with much larger radars used on demanding platforms, such as planes, boats, and tracking systems. Here, because the resolution of any radar depends heavily on the stability of its interrogating signal, the quality of the internal oscillator that generates this signal is among the most important determinants of radar performance. It is for this reason that the most capable radars use frequency signal generators based on 'Poseidon' oscillators that derive their stability from bulky (and expensive) sapphire-loaded cavity resonators. However, the size and cost of this approach restricts it to use in large non-portable applications. The research herein breaks this paradigm by recognizing that an oscillator referenced to an ensemble of tiny mechanically resonant structures constructed in diamond material can potentially equal and perhaps outperform a Poseidon oscillator, all in a substantially smaller form factor. Indeed, sizes small enough to enable high-resolution personal radar might be within reach, and this could enable a host of new personal capabilities, including ranging, remote location services, and local area sensing to identify opportunities, e.g., sales on interesting items, favorite foods, etc., as one walks past them.The research specifically explores parametric mechanical frequency division using micromechanical resonators and sub-20-nanometer electrode-to-resonator gaps that together propel the short-term stability and figure-of-merit of oscillators towards that of the best radar oscillators, but in substantially smaller size. Here, tiny electrode-to-resonator gaps enabled by advances in nanofabrication technology increase the electromechanical coupling of capacitive-gap transduced micromechanical resonators to ranges that support gigaHertz oscillators, all while retaining their record-setting quality factors, both of which drive down phase noise and power consumption. Sub-20-nanometer gaps also permit wider frequency tuning, as well as the use of parametric excitation at higher resonance frequencies, which in turn enables mechanical approaches to reducing phase noise further via a combination of frequency division and close-to-carrier filtering, all with nearly no power penalty. While gap reduction enables unprecedented micromechanical resonator and oscillator performance, it also elucidates fundamental physical limitations expected to manifest more prominently at the nano-scale, including nonlinear noise multiplication, undue injection locking, Casimir forces, enhanced (unwanted) acceleration sensitivity, and less resilience against finite fabrication tolerances and stress. While possibly detrimental to performance, these physical limitations open fertile ground for scientific study. Indeed, lessons learned by modeling the influence of nonlinearity on oscillator limiting and phase noise are likely key to propelling micromechanical oscillators into the stated higher end applications.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.