【作者】 王慧泉；

【导师】 王跃林； 金仲和；

【作者基本信息】 浙江大学 ， 微电子学与固体电子学， 2008， 博士

【摘要】 纳机电谐振器的应用十分广泛,可作为新的实验手段来研究量子物理,并可在高灵敏度传感器和射频电路等方面得到直接应用,因此得到人们广泛关注。在检测方面,随着尺寸的进一步减小,目前应用于纳机电谐振器的电容、压阻等检测方法将遇到信号提取困难,甚至无法工作的问题,必须研究新的检测方法以满足应用需求。论文提出一种新型场效应管检测方法,即将谐振器作为源区、沟道区和漏区,SOI硅片衬底作栅电极,构成空气间隙场效应管,利用沟道电流检测谐振器振动,不管谐振器尺寸多大,该效应均存在,是一种有效的纳机电谐振器检测方法。建立了初步的理论模型,分析表明,沟道电流可反应振动情况,二倍频分量最易检测振动;发现了由机械振动引起场效应管输出特性曲线中的负阻现象,并在实验中得到验证。采用等离子体处理工艺解决了掏空后器件不能正常工作的问题。在源、漏电极和栅极间增加去寄生电极有效地消除了寄生信号。在制作方面,随着纳机电谐振器由梁结构进一步发展为线结构,目前标准的纳米线加工方法不适于批量制作,而新发展的一些利用材料和工艺特性的加工方法,或工艺、版图设计较复杂,或器件尺寸不容易控制,发展工艺简单可靠、可精确控制尺寸的加工方法是纳机电谐振器进一步发展迫切需要解决的问题。论文在制作梁式谐振器时首次发现了含HF酸溶液选择性腐蚀PN结N型区域现象,对腐蚀机理进行了探讨。常温下腐蚀速率小于1nm/min,腐蚀后样品表面非常光滑,可用于纳米结构的加工。基于该现象发展了一套纳机电谐振器加工工艺,完全采用标准MEMS工艺,工艺简单,通过控制初始SOI硅片顶层硅厚度和BOE腐蚀时间可精确控制纳米线尺寸,利用该工艺制作了宽和厚50nm左右的谐振器结构。刘等人提出了一种基于TMAH各向异性腐蚀的谐振器加工工艺,控制氧化厚度及TMAH腐蚀时间可精确控制尺寸。但是该工艺采用氮化硅作TMAH腐蚀的掩膜,而生长和刻蚀氮化硅需要采用LPCVD和Ion Beam,工艺较复杂。论文采用氧化硅取代氮化硅作TMAH各向异性腐蚀掩膜,改进了该工艺,制作了几百纳米宽,几十纳米厚的样品。对实际应用来说,噪声是制约谐振器性能的重要因素;而辐射损伤则是航空航天领域应用必须解决的问题。目前多数研究者将辐射导致的微/纳器件性能改变归因于电学性能的改变,而对辐射引起器件机械性能的改变则较少涉及,这对谐振器这类强烈依赖结构机械性能的器件来说,是不够的。论文建立了初步的微/纳机电谐振器噪声模型,仿真分析表明对于微机电谐振器及目前常见的纳机电谐振器来说,谐振频率附近噪声主要由布朗噪声引起,远离谐振频率处噪声由随机温度漂移噪声、Johnson噪声及布朗噪声共同决定。高真空、超低温条件可获得较好的噪声性能。对微/纳机电谐振器进行了电子和钴60γ射线辐射实验,测得了谐振频率、Q值等机械性能变化,并且这些变化在常温下可退火。对结果进行了初步分析,辐射在材料内部引入缺陷,引起内应力,改变内耗,导致材料机械参数变化,引起谐振器谐振频率漂移,Q值变化;电子辐射以及钻60γ射线辐射引起的缺陷不是永久的,在常温下可退火。本文提出了一种新型纳机电谐振器检测方法,即场效应管检测方法,该方法不受谐振器尺寸的限制;发展了一套基于BOE溶液选择性腐蚀PN结N型区域现象的纳机电谐振器加工工艺,其工艺简单,并可精确控制谐振器尺寸;改进了刘等人提出的基于TMAH各向异性腐蚀的纳机电谐振器加工工艺;建立了初步的谐振器的噪声模型;对微/纳机电谐振器进行了电子和钴60γ射线辐射实验,并对实验结果进行了初步分析。通过本论文的工作,为纳机电谐振器的进一步发展打下了良好的基础,为提高微/纳机电谐振器性能,推动微/纳机电谐振器在航空航天领域的应用提供了理论依据。更多还原

【Abstract】 Nowadays, it is possible to produce NEMS resonators with dimensions well below 100nm, which show increased eigenfrequencies up to 1GHz. In this frequency range NEMS resonators could serve as filters for information processing applications. Another range of applications emerges from the sensitivity these devices could reach in sensor applications. Using sophisticated detection schemes this might even lead to the quantum limit where e.g. the uncertainty principle might be observed in the motion of a mechanical resonator. NEMS resonators have drawn lots of attention because of these applications. However, as the dimension is so small, it is difficult to develop fabrication and detection method for NEMS resonator. MEMS and NEMS resonators are suitable for aeronautical and astronautical application because of their small size and low power consumption. But there is radiation in the outer space, mechanical property of the resonator will change due to radiation. A little research work has been done on this area.This work has done some researches on fabrication and detection method for NEMS resonators, noise characteristic and mechanical radiation damage for MEMS/NEMS resonators.Crystal-silicon nano-beam, with one hundred nanometers thickness, is fabricated on the top silicon of N-type SOI wafer. PNP junction is formed on the beam. P-channel air-gap thin film transistor （TFT） is obtained after the oxide layer under the beam removed, with the PNP junction as drain, channel and source, and the substrate of the SOI wafer as gate. Such an air-gap TFT can be used for vibration detection of the silicon beam. The electric characteristic of the as-released air-gap TFT is very poor. After treated in O₂ and N₂ plasma for 5 minutes, the characteristic is significantly improved. Negative resistance phenomenon in the output curve because of the beam motion is observed.It is found that n-type area of pn junction can be selectively etched by BOE solution without illumination, with etching rate lower than 1nm/min. The possible mechanism of the etching phenomenon is discussed. A simple fabrication process for NEMS resonator is proposed according to the above phenomenon. In this process only traditional micro-electromechanical system technology is used. Dimension of the fabricated nano-wire can be controlled well. A 50nm wide and 50nm thick resonator has been formed using this method.Liu et al developed a fabrication process for NEMS resonator based on TMAH anisotropic etching. Si₃N₄ is used as the etching mask. Using SiO₂, instead of Si₃N₄, as the etching mask, a NEMS resonator, with a few hundreds nanometer width and a few tens nanometer thickness is successfully fabricated. The fabrication process is more simple and easier to control.A simple noise model for MEMS/NEMS resonator is established. Simulation results indicate that the noise near the eigenfrequencies is determined by the Brownian noise, but the noise far from the eigenfrequencies is determined by the temperature fluctuation noise, Johnson noise and the Brownian noise. The noise becomes small when the resonator works at high vacuum and low temperature.Changes in the eigenfrequencies and Q of the MEMS/NEMS resonator have been detected by the electron and gamma ray radiation experiment. A simple mechanical radiation damage theory is established based on these results. Disfigurement will be produced in the semiconductor material by radiation. The disfigurement is unabiding and it can be annealed at room temperature.更多还原