High-Tc superconducting THz emitters fabricated by wet etching

Yuuki Shibano,Takanari Kashiwagi,Yuki Komori,Takashi Yamamoto,Richard A Klemm,Kazuo Kadowaki,Hidetoshi Minami,Kazuki Sakamoto,Yuki Tanabe

doi:10.1063/1.5061682

Abstract

We studied the etching of small crystals of the high-Tc superconductor Bi2Sr2CaCu2O8+δ (Bi2212) with various dilute compositions of hydrochloric and nitric acids. A particular mixture of those acids was chosen to simultaneously fabricate multiple rectangular stand-alone Bi2212 mesa structures from a large, doubly-cleaved and doubly metallic-coated single crystal. The radiation characteristics of these devices were found to be very similar to stand-alone devices fabricated previously using dry-etching techniques. The greatly reduced time and cost of fabrication of stand-alone Bi2212 devices using our wet-etching technique should facilitate the mass production of a large number of identical stand-alone devices from a large single-crystalline Bi2212 substrate.

Highlights

In a single crystal of the high-Tc superconductor Bi2Sr2CaCu2O8+ δ (Bi2212), the superconducting CuO2 layers sandwiched by the insulating Bi2O2 layers are stacked along the crystallographic c-axis
We studied the effects of wet-etched Bi2212 single crystals using several different etching solutions
The results clearly showed that either some of the dilute concentrations of HCl or certain mixtures of diluted HCl and HNO3 can be used as an effective etchant of Bi2212 single crystals

Summary

INTRODUCTION

In a single crystal of the high-Tc superconductor Bi2Sr2CaCu2O8+ δ (Bi2212), the superconducting CuO2 layers sandwiched by the insulating Bi2O2 layers are stacked along the crystallographic c-axis. Several groups recently reported wet-etching fabrication methods of mesa structures from Bi2212 single crystals.[23–25]. Based upon those studies,[23–25] we extended their wetetching methods to fabricate stand-alone mesa (SAM) structures. A SAM does not have a superconducting substrate underneath it, its top and bottom surfaces are coated with gold, providing more efficient self-generated heat exhaust from the mesa devices, and increasing the device’s output radiation power and frequency range. These characteristics were predicted theoretically[26,27] and have been confirmed experimentally.[9–12]. The wet-etched SAM device characteristics are shown to be consistent with those obtained from SAMs fabricated using the more expensive and time-consuming dry-etching methods

WET-ETCHING STUDIES OF Bi2212 SINGLE CRYSTALS

FABRICATION OF SAMS BY WET ETCHING

RADIATION CHARACTERISTICS OF A SAM FABRICATED BY WET ETCHING

SUMMARY