Fabrication of Spatially Confined Complex Oxides

Summary

We describe the use of pulsed laser deposition (PLD), photolithography and wire-bonding techniques to create micrometer scale complex oxides devices. The PLD is utilized to grow epitaxial thin films. Photolithography and wire-bonding techniques are introduced to create practical devices for measurement purposes.

Abstract

Complex materials such as high Tc superconductors, multiferroics, and colossal magnetoresistors have electronic and magnetic properties that arise from the inherent strong electron correlations that reside within them. These materials can also possess electronic phase separation in which regions of vastly different resistive and magnetic behavior can coexist within a single crystal alloy material. By reducing the scale of these materials to length scales at and below the inherent size of the electronic domains, novel behaviors can be exposed. Because of this and the fact that spin-charge-lattice-orbital order parameters each involve correlation lengths, spatially reducing these materials for transport measurements is a critical step in understanding the fundamental physics that drives complex behaviors. These materials also offer great potential to become the next generation of electronic devices ^1-3. Thus, the fabrication of low dimensional nano- or micro-structures is extremely important to achieve new functionality. This involves multiple controllable processes from high quality thin film growth to accurate electronic property characterization. Here, we present fabrication protocols of high quality microstructures for complex oxide manganite devices. Detailed descriptions and required equipment of thin film growth, photo-lithography, and wire-bonding are presented.

Introduction

The first and one of the most important steps towards high quality devices is the growth of epitaxial oxide thin films. A single crystal substrate is used as a "template" to deposit the target materials. Among different deposition methods, pulsed laser deposition (PLD) is one of the best ways to acquire good quality thin films ^4,5. The growth processes involve heating the substrate to around 800 °C in an oxygen environment and using laser pulses to hit the target material and generate a flux to be deposited onto the substrate. The typical system is shown in Figure 1.

While unpatterned films have been shown t....

Protocol

1. Sample Growth Fabrication

1. Clean a 5 mm x 5 mm x 0.5 mm single crystal substrate having a miscut angle <0.1 degree such as SrTiO₃ or LaAlO₃ with acetone and then water in an ultrasonic cleaner for 10 min each. To get a TiO₂ termination on SrTiO₃, etch the substrate in 10% hydrogen fluoride for 30 sec and rinse in water for 1 min, followed by an anneal at 1,100 °C for 10 hr. After cleaning, mount the substrate on a heater suitable for ultra-high vacuum conditions.
2. Mount the heater into the PLD vacuum chamber and open the chamber oxygen source to fill the chamber with 2 x 10E-5 Torr oxygen. Raise th....

Results

This paper focuses mostly on the photolithography and wire-bonding aspects of sample preparation. More details on film growth procedures can be found in our other recent publications ⁸.

Photolithography is an important method to control dimensionality in complex oxides for the purpose of investigating electron correlation lengths and electronic phase separation ^9-13. Figure 2 shows optical images of partial steps during the process. It is necessary to poi.......

Discussion

Unlike single element semiconducting materials such as Si, the fabrication of complex materials can be more difficult due to the fact that the complex structure and multiple elements must all be taken into consideration. The use of photolithography to fabricate complex oxide devices is relatively low cost and fast to prototype as opposed to other confinement techniques. There are however some important limitations to understand. Photolithography has a spatial limitation to creating structures of about 1 micron so is not .......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Reagent/Material
SrTiO3(001) & LaAlO3(100) substrates	CrysTec GmbH
Microposit S1813 Photoresist	Shipley
CD-26 Developer	Shipley	38490
GE varnish	Lakeshore	VGE-7031
Equipment
Reflected High Energy Electron Diffraction (RHEED)	Staib Instruments		35kV TorrRHEED
Mask Aligner	ABM	Model 85-3 (350W) Lightsource
Resistivity Puck	Quantum Design	P102
Wire Bonder	Kulicke Soffa	04524-0XDA-000-00