Measurements of thermodynamical physical properties of High Tc Superconducting Thin Film

本研究主要研究了以下三个问题：A.薄膜Bi-Sr-Ca-Cu-O的交流阻抗在许多基于高温（高TC）超导体（HTS）的电子器件中，薄膜HTS总是经受交流（AC）或脉冲电流。与此相反，我们的工作集中在阻抗z的大小和相位的大值J。实验进行了Bi-Sr-Ca-Cu-O外延膜。结果表明，在500 kHz及以上的频率范围内，z值随频率的增加而增加。这些结果可以通过假设薄膜中存在磁通涡旋来定性地解释。金属点接触的热传递和热电电压由于已经证明，即使是相似的金属之间的点接触（PC）也可以产生热电电压，因此将PC用作微型温度传感器似乎很有前途。在从85 K到室温的温度范围内，热电电压被证明存在，即使 ...更多信息 在Ag-Ag PC中，根据先前的结果。这个热电电压是方便地绘制对无量纲基板温度，证明了采用PC作为温度传感器的可行性。结果表明，在小温降时，沿金属晶须沿着的热流密度与沿PC的温降成线性关系，而在大温降时，沿金属晶须的热流密度与沿PC的温降成非线性关系。Er-Ba-Cu-O高TC超导薄膜的薄膜/衬底界面热阻低温下薄膜高TC电子器件的热设计和工作关键取决于薄膜和衬底界面处的接触热阻（Rbd）。在我们的实验研究中，用一种将超导膜腐蚀成两个相邻的条带的技术测量了沉积在MgO衬底上的Er-Ba-Cu-O超导膜的Rbd。一条带支持大的偏置电流并用作加热器，而另一条带携带小得多的电流，并用于测量衬底的温度。从我们的研究结果得出的主要结论是，Rbd至少比以前报道的值高两个数量级。少

Following three subjects have been investigated.A. AC Impedance of Thin-Film Bi-Sr-Ca-Cu-OIn many electronic devices based on high-temperature (high-TC) superconductors (HTS), the thin-film HTS are invariably subjected to an alternating (AC) or pulsed current. In contrast, our work concentrated on the magnitude and phase of impedance z for large values of J. Experiments were conducted on an epitaxial film of Bi-Sr-Ca-Cu-O. The results indicated that for 500kHz and above, z increased with increasing frequency. These results could be qualitatively explained by assuming that magnetic flux vortices were present in the film.B. Heat Transfer and Thermoelectric Voltage at Metallic Point ContactsSince it had already been demonstrated that a Point-contact (PC) between even similar metals can generate a thermoelectric voltage, the use of PC's as microscale temperature sensors seemed promising. At temperatures ranging from 85 K to room temperature, a thermoelectric voltage was shown to exist even … More at the Ag-Ag PC, in accordance with the previous results. This thermoelectric voltage was conveniently plotted against the nondimensionalized substrate temperature, demonstrating the feasibility of employing a PC as a temperature sensor. It was shown that the heat flux along the metal whisker is a linear function of the temperature drop across the PC for small temperature drops, but becomes nonlinear for large temperature drops.C. Film/Substrate Thermal Boundary Resistance for an Er-Ba-Cu-O High-TC Superconducting FilmThe thermal design and operation of thin-film high-TC electronics at low temperatures depends crucially on the thermal contact resistance at the boundary between the film and the substrate (Rbd). In our experimental investigation, Rbd for an Er-Ba-Cu-O film deposited on an MgO substrate, was measured by a technique in which the superconducting film was etched into two adjacent strips. One strip supported a large bias current and served as the heater, while the other strip carried a much smaller current, and served to measure the temperature of the substrate. The principal conclusion drawn from our results was that Rbd was at least two orders of magnitude higher than the previously reported values. Less