Please cite this article in press as: M. Sojková, et al., Patterning of Tl-based superconducting films using new etching solution, Appl. Surf. Sci. (2014), http://dx.doi.org/10.1016/j.apsusc.2014.02.183 ARTICLE IN PRESS G Model APSUSC-27400; No. of Pages 4 Applied Surface Science xxx (2014) xxx–xxx Contents lists available at ScienceDirect Applied Surface Science jou rn al h om ep age: www.elsevier.com/locate/apsusc Patterning of Tl-based superconducting films using new etching solution M. Sojková ∗ , V. ˇ Strbík, M. ˇ Spanková, ˇ S. Chromik Institute of Electrical Engineering, SAS, Dúbravská cesta 9, 841 04 Bratislava, Slovakia a r t i c l e i n f o Article history: Received 22 January 2014 Received in revised form 28 February 2014 Accepted 28 February 2014 Available online xxx PACS: 74.72.Jt 74.78.Bz 74.62.Bf Keywords: Tl-based superconductors Thin films CeO2 buffered R-plane sapphire LaAlO3 Structures Wet etching a b s t r a c t Tl-based cuprate superconducting films were prepared in a two-step process by RF magnetron sputtering of an amorphous precursor and ex situ thallination in open system. The films prepared on LaAlO 3 and CeO 2 buffered R-plane sapphire substrates consisted from c-axis oriented Tl-2212 superconducting phase. The zero resistance critical temperature T C0 exhibited values up to 94 K. Subsequently, superconducting structures were prepared from the Tl-based thin films using photolithography process and wet etching. A new etchant based on potassium iodide was used for the Tl-based film patterning. The prepared structures had sharp edges, unchanged phase composition and critical temperature values. Such a way of the Tl- based film patterning is very simple, fast and easy to realize. © 2014 Elsevier B.V. All rights reserved. 1. Introduction Thin films of thallium based high temperature superconduc- tors (HTS) can be used in a wide range of applications thanks to their high values of critical temperatures. Tl-based cuprates constitute one of the largest chemical families of HTS. Because of relatively high zero resistance critical temperature T C0 (up to 110 K), stronger resistance to moisture and higher structure stabil- ity Tl 2 Ba 2 CaCu 2 O 8 (Tl-2212) films are a very promising material for devices [1]. In addition, Tl-2212 can be easily synthesized in a single phase and the prepared films exhibit a good stability in an ambi- ent environment [2]. Higher T C0 value of Tl-based superconductors compared with YBa 2 Cu 3 O 7 means that thermally activated flux motion of the Tl-based superconductor is less probable at the criti- cal temperature of YBa 2 Cu 3 O 7 . This is important for low frequency applications where 1/f noise caused by flux motion is dominant [3]. It is expected that the first commercial application of Tl-based superconducting films could be found in the area of passive microwave devices. Thin films deposited onto low-loss substrates ∗ Corresponding author. Tel.: +421 2 5922 2240; fax: +421 2 5477 5816. E-mail addresses: michaela.sojkova@savba.sk, sojkova.michaela@gmail.com (M. Sojková). (such as LaAlO 3 (LAO), sapphire) have low values of surface resis- tance and high quality factors [3]. Potential applications include channel filters for ground- and satellite-based communications systems, low-phase-noise oscillators for digital communications and radar systems and receive coils for medical diagnosis equip- ment. To use these thin films for applications, it is necessary to pattern them into convenient structures. There are only a few publications concerning Tl-based films patterning. The most used way of patterning the Tl-based films is reactive ion etching [4], ion beam etching and focused ion beam are also mentioned in several publications [5,6]. However, these meth- ods are relatively expensive and technically demanding. Moreover, the thickness of the film is limited to about 50–100 nm because of fast degradation under ion bombardment. Lift-off technique is based on the precursor film patterning and subsequent thallina- tion [7]. However, thallination is a very complex process and the precursor films are often degraded during resist removal making this method in some cases irreproducible. There is a lot of different etchants used for wet patterning of the Tl-based films. The main problems of this method are degrada- tion of the superconducting film or the resist, selective etching or underetching. Several etchants like di- and tricarboxylic acids [8], ethylendiamintetraacetic acid and its sodium salts [9] have been used successfully; however, the maximum etching rate is 1 nm/s. http://dx.doi.org/10.1016/j.apsusc.2014.02.183 0169-4332/© 2014 Elsevier B.V. All rights reserved.