A Critical Analysis of Techniques and Basic Phenomena Related to Deposition of High Temperature Superconducting Thin Films

The processes involved in plasma and ion beam sputter-, electron evaporation-, and laser ablation-deposition of high temperature superconducting thin films are critically reviewed. Recent advances in the development of these techniques are discussed in relation to basic physical phenomena, specific to each technique, which must be understood before high quality films can be produced. Low temperature processing of films is a common goal for each technique, particularly in relation to integrating high temperature superconducting films with the current microelectronics technology. Research is now demonstrating that the introduction of oxygen into the growing film, simultaneously with the deposition of the film components, is necessary to produce as-deposited superconducting films at relatively low substrate temperatures

Domain Wall Enabled Hysteresis-Free Steep Slope Switching in MoS2_2 Transistors

The device concept of operating ferroelectric field effect transistors (FETs) in the negative capacitance (NC) regime offers a promising route for achieving energy-efficient logic applications that can outperform the conventional CMOS technology, while the viable mechanisms for stabilizing the NC mode remain a central topic of debate. In this work, we report hysteresis-free steep slope switching in few-layer and bilayer MoS$_2$ transistors back-gated by single layer polycrystalline PbZr$_{0.35}$Ti$_{0.65}$O$_3$ films. The devices exhibit current on/off ratios up to 8$\times$10$^6$ within an ultra-low gate voltage window of V$_g$ = $\pm$0.5 V and subthreshold swing as low as 9.7 mV/decade at room temperature, transcending the 60 mV/decade Boltzmann limit. Unlike previous studies, the quasi-static NC mode is realized in a ferroelectric without involving an additional dielectric layer. Theoretical modeling reveals the dominant role of the metastable polar states within ferroelectric domain walls in enabling the NC mode in the MoS$_2$ transistors. Our findings shed light into a new mechanism for NC operation, providing a simple yet effective material strategy for developing high speed, low-power 2D nanoelectronics.Comment: 15 pages, 5 figure

Critical Role of Suspension Media in Electrophoretic Deposition: The Example of Low Loss Dielectric BaNd2Ti5O14 Thick Films

The importance of electrophoretic deposition (EPD) is well recognized for thick film technology, but unfortunately there is no universal suspension medium for the EPD of oxides. Thus, the selection of the medium, the stability of the suspensions, and the control of the particle potentials, critical for a good deposition, need to be established for each new material being processed by EPD. In this article, we investigate the key parameters, studying the electrochemistry of BaNd2Ti5O14 (BNT) suspensions, and establish relationships between suspension media, EPD process conditions, microstructure of the deposits, and resulting electrical properties of the BNT films. Suspension stability of water, ethanol, acetic acid, and acetone-based media was analyzed in terms of zeta potential, particle size distribution, UV transmittance, and inductively coupled plasma spectrometry. The highest absolute zeta potential values determined for acetone with I-2 and acetic acid media are in good agreement with the high stability, small and narrow particle size distribution, and low UV light transmittance measured for these suspensions. Very high quality thick deposits were consequently achieved. However, it was demonstrated that aging of the acetic acid-based suspension have serious negative effects on the EPD process for BNT materials, including leaching of the metallic elements with a consequent modification of the material stoichiometry, change of the conductivity of the suspension, and degradation of the films microstructure. These facts severely restrict the use of acetic acid. Our results clearly indicate that, besides the stability of the suspension, the electrochemistry and aging behavior are key aspects for the EPD of functional oxides. Our systematic approach could be viewed as providing a set of guidelines for the development of EPD of other oxides

Ferroelectric behavior in nominally relaxor lead lanthanum zirconate titanate thin films prepared by chemical solution deposition on copper foil

We demonstrate that (Pb0.9La0.1)(Zr0.65Ti0.35)0.975O3 (PLZT) (10/65/35) thin films that have a nominally relaxor composition and that are deposited by chemical solution deposition onto copper foil show polarization hysteresis. Ferroelectric domain switching and a shift in Curie temperature are also observed. This is in contrast to the non-hysteretic behavior of films with identical composition prepared on Pt/SiO2 / Si substrates. This suggests that the mismatch in coefficient of thermal expansion between PLZT and copper induces a compressive strain in the PLZT during cooling after high temperature crystallization under low pO2, and causes an out-of-plane polarization

Electrophoretic Deposition on Nonconducting Substrates: A Demonstration of the Application to Microwave Devices

Through the use of a sacrificial carbon layer, this work reports a method of performing electrophoretic deposition (EPD) of thick films on fully nonconducting substrates, overcoming the restricting requirement for EPD of a conducting or partially conducting substrate. As a proof of concept, the method was applied to the development of microwave thick films on insulating alumina substrates. The key parameter to be controlled is the thickness of the sacrificial carbon layer; this is expected to be a general result for the application of the processing method. The method allows direct pat terning of the structure and leads to the potential use of EPD in a far wider range of electronic applications (multilayer ceramic capacitors (MLCCs), low temperature cofired ceramics (LTTCs), and biotech devices). Furthermore, in conjunction with work reported elsewhere, the development of specific BaNd2Ti5O14 (BNT) thick film microwave dielectrics opens up a technology platform for a range of high quality factor (Q) devices. More specifically, 100 μm thick BNT layers were achieved with a dielectric constant of 149 and Q of 1161 (10 GHz). These materials can now be integrated with tunable dielectrics or dielectrics on metal substrates to provide a platform for devices in the front end of communication systems and cellular base stations

Microstructural studies of PZT thick films on Cu foils

This paper explains the limits of processing conditions for Pb(Zr, Ti)O3 (PZT) thick films on Cu substrates. PZT thick films in the thickness range 5–20 μm deposited on flexible Cu foils by electrophoretic deposition showed poorer properties when compared with PZT thick films deposited on Pt foils under identical conditions. Although the density of the sintered films and the electrical properties were improved by introducing a PbO coating on the top of the films, the dielectric and ferroelectric properties of PZT thick films on Cu were still inferior to those of films deposited on Pt. Rutherford backscattering spectrometry, X-ray diffraction and transmission electron microscopy revealed the formation of a Cux–Pb alloy when sintering above 950 °C, accompanied by Ti enrichment of the PZT and the formation of ZrO2 phases. As the sintering temperature increased, the concentration of the metallic phase increased and spread throughout the film. A new Pb–Cu alloy phase was identified. The poorer electrical properties of PZT thick films on Cu were correlated with these microstructural features