Adam Chamberlain

University of Missouri-Rolla

Ceramic Engineering

Hydrothermal Processing of BaxSr(1-x)TiO3

Introduction

Barium strontium titanate's (BST) tunable dielectric constant (k') high dielectric strength, low leakage and loss (tand has made it desirable for a variety of electrical applications including the following: dynamic random access memory (DRAM); microelectromechanical systems (MEMS); multilayer capacitors. Conventional methods of producing BST are sputtering, metal-organic vapor deposition (MOCVD), and chemical solution deposition (CSD). These methods however sometimes require high vacuum systems or heat treatments that can exceed 500oC.1-5 In using a hydrothermal process crystalline BST is produced at temperatures below 100oC by using an aqueous medium. In using this process thin films have been produced that had dielectric constants from 100 to 185 and loss values of 0.25.6

Objectives

  • Measure dielectric constant, tandand leakage as a function of composition and annealing.
  • Process BST thin films below 100 nm using the hydrothermal process.
  • Observe the effect of dopants in hydrothermal BST thin films.

Approach

  • BST thin films were produced using a hydrothermal process used by Mark McCormick at Purdue University. Various Ba,Sr(OH(2 solutions were made ranging from 20-90% Ba(OH)2, which results in thin films with compositions ranging from 12-78% Ba.
  • From each specimen the following samples were acquired: as formed; oxygen and argon anneal at 500oC.
  • Using an LCR meter an Ac field was applied in order to measure capacitance and tand
  • To measure leakage a Dc voltage was applied using a Keithley 238.
  • To process thin films below 100 nm the metalorganic precursor was diluted using xylene until a noncontinuous film was obtained after reaction. In order to obtain a small grain size a 1.5M Ba(OH)2 solution was used in this reaction.
  • To observe the effects of dopants approximately five atomic percent of magnesium was added to the metalorganic precursor.
Accomplishments
  • Observed that leakage and dielectric constant are not effected by composition.
  • Observed that leakage and dielectric constant decrease when annealed under argon and oxygen.

Leakage current vs. annealing (Data
from 30% barium film).

  • Processes a thin film with a thickness approximately 80 nm using the hydrothermal process.
  • Processed BST thin films with five atomic percent magnesium.

Figure 1. Barium Titanate Thin Film (~80 nm).
Figure 2. Planar View of Barium Titanate Thin Film.
Final Research Presentation