在次毫米波段的太空觀測研究之中, 尋找一個低雜訊的觀測元件是令許多科學家極感興趣的。我們藉由本實驗室已發展成熟的鈮/氧化鋁/鈮超導穿隧結之製程技術, 進而發展出一套新的製程方法來製作次微米尺度超導穿隧結之混頻元件。 因為此一元件的寄生電容具有可被忽略的特性, 因而能夠在高頻的訊號源之下仍保有較好的匹配效應, 除此之外亦可在較廣的頻寬範圍內操作。 我們使用一般在鈮/氧化鋁/鈮超導穿隧結之製程中所常用到的自動對正的方法先製作出三夾層的結構, 再配合電子束微影技術, 便可精確製作出0.4um×0.4um大小的超導穿隧結。 我們所製作出來的樣品具備低滲漏, 高超導電流密度, 以及觀察其電流-電壓特性曲線之中, 當外加電壓接近超導能隙電壓時, 會出現十分陡峭的非線性行為。樣品的wRnC乘積值為2.4。
我們首度嘗試使用電子束微影技術中不可或缺的PMMA搭配積體電路產業上常用的polymide, 並成功製作出高品質的次微米尺度超導穿隧結。 我們所發展的這套製程可達到~0.1um×0.1um, 甚至到更小的尺度範圍。

在次毫米的量測中, 我們所使用的接收器是選擇波導管耦合超導穿隧結的方式組裝而成。 關於量測結果方面,一個0.2um^2穿隧介面大小的樣品被測量出具有25hv/k的雜訊溫度值。 由於此一樣品的超導電流密度僅有3,250A/cm^2, 因此很難期待會有好的表現。 如何增加樣品的超導電流密度值, 而且同時顧及介面的強韌度, 是爾後需要努力下工夫的地方。

We are interested in the low noise heterodyne receiver used for the astronomical study in the submillimeter wavelengths range and develop a process to fabricate Nb-based superconductor-insulator-superconductor (SIS) junctions with sub-micron size for the purpose of the reduction in the coupling losses at higher radio frequency (RF) and wide bandwidth operation. We use conventional self-aligned mask trilayer process in addition with E-beam lithography to fabricate SIS junctions with well-defined size of ~0.4um×0.4um and high quality, such as low leakage, high current density of ~10kA/cm^2, and sharp nonlinearity in the I-V curve. The junction has wRnC product value of 2.4.
We first attempt to use PMMA combined with polymide, which is commonly used in the IC process, and successfully fabricate sub-micron SIS with high quality. By this process, the junction size could reach ~0.1um×0.1um and even smaller.

Our SIS receiver’s system is waveguide coupled with SIS junction. Under the 300GHz frequency range measurement, a 0.2um^2 area size junction with supercurrent density of 3,250A/cm^2 performs its noise temperature of about 25hv/k. To improve the SIS mixer junction qualities, especially to increase the supercurrent density with a tough junction, is important for the future studies.

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