基于PMMA波导的乐甫波器件特性研究

【作者】 胡佳；

【导师】 谢光忠；

【作者基本信息】 电子科技大学 ， 光学工程， 2008， 硕士

【摘要】 化学传感器在实时监控、分析的需求驱动下,发展得越来越快。如今,声表面波(Surface Acoustic Waves, SAWs)器件已广泛地应用于化学传感器。然而现在常用的瑞利波(Rayleigh Wave)模式无法为一些特殊的用途提供足够高的灵敏度,例如在战场环境下检测化学战剂。为了解决这个问题,本文对双端谐振型乐甫波器件的设计和制备进行了研究,主要的研究结果和结论如下所示:(1)根据声表面波器件的理论,设计和制备了双端谐振型和延迟线表面浅体波(surface skimming bulk waves, SSBWs)器件。为便于比较,两者采用相同的叉指换能器(interdigital transducers, IDTs)的图案。实验结果表明,谐振型器件与延迟线相比,可有效降低插损(谐振型:38.8dB,延迟线:47dB),提高Q值(谐振型:594,延迟线:230),提高了器件的频率稳定性。(2)改良了现有的旋涂工艺:采用低浓度溶液,以提高薄膜表面的平整度;在基片四周制备台阶,在旋涂过程中阻挡溶液散开,以便提高薄膜厚度。经过实验获得了厚度0.8?3.3μm,表面平整度高的PMMA薄膜,并研究了工艺参数对薄膜厚度和平整度的影响。结果表明:溶液浓度、低速档转速和持续时间对薄膜厚度影响最大;低速档与高速档转速之差与低速档持续时间对薄膜表面平整度也具有较大的影响。改良后的旋涂工艺具有较好的可重复性。(3)根据上述工艺,在SSBW器件表面沉积了PMMA波导层薄膜,从而得到乐甫波器件。研究了波导层厚度对乐甫波器件的频率、插损、Q值和质量灵敏度的影响。由于机电耦合系数的增大和波导层对声波能量的有效传输,插损起初随着波导层厚度的增大而减小,在1.3μm达到最低点后,随着机电耦合系数的减小以及波导层的声吸收增加,插损随厚度增大而增大。而Q值的变化规律正好与插损相反。谐振型乐甫波器件相对延迟线而言,可进一步减小插损,提高Q值,但质量灵敏度保持一致,当波导层厚度为2.25μm时,质量灵敏度达到1179cm2 g?1。更多还原

【Abstract】 Chemical sensor development is being increasingly driven by the need for real time analyses. Nowadays, the use of surface acoustic devices as chemical sensors is well known. However, as a common acoustic mode, Rayleigh wave can’t provide enough sensitivity to satisfy several special applications, for example, detection of chemical war agents in battlefield environments. To resolve the problem, the design and fabrication of Love wave resonator devices have been investigated in the dissertation. The chief results and conclusions obtained are as follows:(1)According to SAW theory, the Surface skimming bulk waves(SSBWs) resonator and delay line devices are designed and fabricated. For comparison, both of them have the same pattern of interdigital transducers(IDTs). Compared with delay line, the resonator has the lower insertion loss(resonator: 38.8dB; delay line: 47dB) and higher Q value(resonator: 594; delay line: 230), which enhances the frequency stability of devices.(2)The spin coating technology is modified: the solutions with low concentration is chosen to obtain the layer with a smooth surface; the steps are formed on the edges of substrate to raise the thickness of layer obtained during the spin coating process. In experiments, the PMMA layers with thickness of 0.8?3.3μm are obtained. The thickness of layers depends on the spin speed and the concentration of solution. The roughness of layers depends on the lasting time of the low speed and the difference between the low speed and high speed. The modified spin coating technology also shows nice repeatability.(3) The Love wave devices are obtained by spin coating PMMA guiding layer on the surface of SSBW devices. The properties of devices, such as, frequency, insertion loss, Q value and mass sensitivity are studied as a function of the guiding layer thickness. And then the properties of resonator and delay line devices are also compared. Due to the enhancement of the electromechanical coupling and the efficient guiding of acoustic energy in the guiding layer, insertion loss initially decreases with increasing guiding layer thickness and reaches the minimum at 1.3μm. At the greater thickness, decrease in coupling and the acoustic absorption of guiding layer results in the increase of insertion loss. But the variation of Q value following the increase of thickness is contrary to that of insertion loss. Compared with delay line, the Love wave resonator devices can further suppress insertion loss and enhance Q value, but shows the same mass sensitivity. The mass sensitivity up to 1179cm2 g?1 is got at the thickness of 2.25μm.更多还原