T. S. Kalkur

Challenges and Opportunities for Multi-functional Oxide Thin Films for Voltage Tunable Radio Frequency/Microwave Components

There has been significant progress on the fundamental science and technological applications of complex oxides and multiferroics. Among complex oxide thin films, barium strontium titanate (BST) has become the material of choice for room-temperature-based voltage-tunable dielectric thin films, due to its large dielectric tunability and low microwave loss at room temperature. BST thin film varactor technology based reconfigurable radio frequency (RF)/microwave components have been demonstrated with the potential to lower the size, weight, and power needs of a future generation of communication and radar systems. Low-power multiferroic devices have also been recently demonstrated. Strong magneto-electric coupling has also been demonstrated in different multiferroic heterostructures, which show giant voltage control of the ferromagnetic resonance frequency of more than two octaves. This manuscript reviews recent advances in the processing, and application development for the complex oxides and multiferroics, with the focus on voltage tunable RF/microwave components. The over-arching goal of this review is to provide a synopsis of the current state-of the-art of complex oxide and multiferroic thin film materials and devices, identify technical issues and technical challenges that need to be overcome for successful insertion of the technology for both military and commercial applications, and provide mitigation strategies to address these technical challenges.

Characteristics of Metal/Ferroelectric/Insulator/Semiconductor Field Effect Transistors Using a Pt/SrBi2Ta2O9/Y2O3/Si Structure

For the fabrication of metal/ferroelectric/insulator/semiconductor field effect transistors (MEFISFETs), SrBi2Ta2O9 (SBT) film was formed onto Y2O3 layer using the metal organic deposition (MOD) method. Memory windows of MEFISFET were in the range of 0.96–1.38 V when the gate voltage varied from 5 to 7 V. Current-voltage characteristic and transconductance curve of the MEFISFET show the effective gate modulation and the stable memory effect induced by the ferroelectric properties.

Strain engineered barium strontium titanate for tunable thin film resonators

Piezoelectric properties of epitaxial (001) barium strontium titanate (BST) films are computed as functions of composition, misfit strain, and temperature using a non-linear thermodynamic model. Results show that through adjusting in-plane strains, a highly adaptive rhombohedral ferroelectric phase can be stabilized at room temperature with outstanding piezoelectric response exceeding those of lead based piezoceramics. Furthermore, by adjusting the composition and the in-plane misfit, an electrically tunable piezoelectric response can be obtained in the paraelectric state. These findings indicate that strain engineered BST films can be utilized in the development of electrically tunable and switchable surface and bulk acoustic wave resonators.

Metal-ferroelectric-semiconductor characteristics of bismuth titanate films on silicon

Bismuth titanate (Bi4Ti3OI2) is one of the well known ferroelectrics which exhibits switchable spontaneous polarization in all directions.l,2 Because of its high Curie temperature of 675 °C and high breakdown strength, it has high potential for device applications. Some attempts have been reported regarding the integration of bismuth titanate into silicon MOSFETS for the implementation of non-volatile memories with limited success.3,4 In addition to this, bismuth titanate has a relatively high dielectric constant.5 Recently, there is tremendous interest in using these high dielectric constant materials for storage capacitors in dynamic random access memory applications (DRAM), and as gate insulators to increase the transconductance of MOSFETS.6-8 Therefore, in this paper we are presenting the results of metal—bismuth titanate- p—Si capacitors for device applications as a high dielectric constant material.

Tunable Ferroelectric Capacitor-Based Voltage-Controlled Oscillator

Ferroelectric capacitors made from Ba10.5Sr0.5 TiO3 (BST) are applied as varactors in tunable, high-frequency circuit applications. In this context, a voltage-controlled oscillator (VCO) has been designed and implemented using discrete RF bipolar junction transistor (BJTs) and tunable ferroelectric capacitor. The designed VCO has a tuning range from 205 MHz to 216.3 MHz with a power dissipation of 5.1 mW. The measured phase noise is -90 dBc/Hz at 100 kHz and -140 dBc/Hz at 1 MHz offset

High-speed current-mode logic amplifier using positive feedback and feed-forward source-follower techniques for high-speed CMOS I/O buffer

A new approach to implement low-power high-performance integrated output pad drivers in monolithic integrated circuits is presented. The design utilizes a source-follower topology along with a simple positive feedback and a simple feed-forward approach to control both rise and fall times for a given loading capacitance. This novel technique is used to implement a differential output pad driver for the high-speed serial data/clock design in a standard 0.13 /spl mu/m CMOS technology. The driver occupies less than 0.12 mm/sup 2/ of die area including the area of two ball pads and can drive 50-/spl Omega/ load through 50-/spl Omega/ transmission line for higher than 12-Gb/s data rates.

Erbium-oxide-based metal-insulator-semiconductor structures on silicon

Abstract Reactively evaporated and thermally oxidized erbium-oxide-based metal-insulator-semiconductor structures have been studied on p-type silicon. Erbium films of thickness 280 A were deposited by electron beam evaporation in an oxygen atmosphere with the substrate held at room temperature. The oxidation of erbium was performed in an atmosphere of dry oxygen by ramping the furnace from room temperature to a final temperature of 700°C. The surface morphology of the erbium oxide was characterized using scanning electron microscopy and the structure was determined by X-ray diffraction. The electrical characterization of the Al/erbium oxide/p-Si was performed using capacitance-voltage and current-voltage measurements.

Dielectric properties of Mg-doped Ba0.96Ca0.04Ti0.84Zr0.16O3 thin films fabricated by metalorganic decomposition method

Mg-doped Ba0.96Ca0.04Ti0.84Zr0.16O3 (BCTZ) thin films have been proposed as a promising material for microelectronic device applications based on high dielectric materials. Perovskite polycrystalline Mg-doped BCTZ thin films were fabricated on a Pt/Ti/SiO2/Si substrate by metalorganic decomposition method. Dielectric properties were improved after a Pt/Mg-doped BCTZ thin film/Pt capacitor was post-annealed at 700 °C in O2 atmosphere for 30 min. A high dielectric constant of 460 at 1 MHz, a low dissipation factor less than 4.5%, and a low leakage current density of 4×10−7 A/cm2 at 3 V were obtained. Improved dielectric properties were discussed in conjunction with reduction of oxygen vacancies and electrons due to the post-annealing and Mg dopants.

Low temperature deposited Ba0.96Ca0.04Ti0.84Zr0.16O3 thin films on Pt electrodes by radio frequency magnetron sputtering

Ba0.96Ca0.04Ti0.84Zr0.16O3 films acceptor doped with Sc were deposited on Pt/TiO2/SiO2/Si substrates using radio frequency magnetron sputtering. Substrate temperatures throughout the fabrication process remained at or below 450 °C, which allows this process to be compatible with many materials commonly used in integrated circuit manufacturing. In addition, this process made no use of oxygen in the sputter gas or in annealing atmospheres and thus it remains compatible with easily oxidized materials. A relative dielectric constant of 166 was achieved along with a loss tangent of 1.9% at 100 kHz. Leakage current densities of 1.6×10−8 A/cm2 were observed at 300 K with 300 kV/cm of applied electric field.

Electrical characteristics of ZrO2-based metal-insulator-semiconductor structures on p-Si

Abstract The metal-insulator-semiconductor characteristics of annealed ZrO2 films and oxidized zirconium films have been compared. The ZrO2 and zirconium films have been deposited by electron beam evaporation. Scanning electron microscopy analysis reveals a smooth morphology for deposited as well as annealed or oxidized films. The X-ray diffraction analysis shows that the as-deposited films are amorphous and become crystalline as a result of annealing. The static dielectric constant was found to be higher for annealed zirconium oxide films as compared with oxidized zirconium films. The dielectric constant was found to be dependent on annealing temperature.