S. W. Kirchoefer

United States Naval Research Laboratory

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J.M. Pond

University of Newcastle Australia

Wontae Chang

United States Naval Research Laboratory

Douglas B. Chrisey

Tulane University

James S. Horwitz

United States Naval Research Laboratory

J. S. Horwitz

Harvard University

S. B. Qadri

United States Naval Research Laboratory

L. M. B. Alldredge

United States Naval Research Laboratory

N. Holonyak

University of Illinois Urbana-Champaign

E. J. Cukauskas

United States Naval Research Laboratory

Jeffrey A. Bellotti

Reflective X Ray Optics

Cooperative Institutions

United States Naval Research Laboratory

Naval Research Laboratory Electronics Science and Technology Division

University of Illinois Urbana-Champaign

United States Navy

Pennsylvania State University

Argonne National Laboratory

K Lab (United States)

Rutgers, The State University of New Jersey

University of Houston

McCormick (United States)

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Room-temperature tunable microwave properties of strained SrTiO3 films

Journal of Applied Physics (2004)

Wontae Chang S. W. Kirchoefer J.M. Pond Jeffrey A. Bellotti S. B. Qadri

Structural distortion of ferroelectric thin films caused by film strain has a strong impact on the microwave dielectric properties. SrTiO3 thin films epitaxially grown on (110)DyScO3 substrates using molecular beam epitaxy are extremely strained (i.e., ∼1% in-plane tensional strain) from 3.905Å of bulk SrTiO3. The room-temperature in-plane dielectric constant and its tuning of the films at 10GHz are observed to be 6000 and 75% with an electric field of 1V∕μm, respectively. The control of strain in SrTiO3 provides a basis for room-temperature tunable microwave applications by elevating its phase-transition peak to room temperature.

Strain (injury)

10.1063/1.1813641

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Citations (31)

High-resolution scanning optical microscopy of ferroelectric thin films

Ferroelectrics (1999)

Jeremy Levy Charles Hubert Adrian C. Carter Wontae Chang S. W. Kirchoefer

Abstract Two optical techniques are used to map the electric polarization in BaxSr1-xTiO3 (BST) thin films at room temperature. The first, confocal scanning optical microscopy (CSOM), is a diffraction-limited technique with wide applicability and ease of use. CSOM images taken at different static electric fields show reorientation of ferroelectric nanodomains. Local hysteresis loops, obtained by cycling the applied electric field at one position on the sample, suggest a coexistence of both paraelectric and ferroelectric phases at compositions x which exhibit paraelectric behavior in the bulk. Non-uniform strain is postulated to account for the apparent spatial variations of the Curie temperature. The second technique, apertureless near-field scanning optical microscopy (ANSOM), is used to image polarization fluctuations with a spatial resolution of 30 Å. ANSOM images of the same samples show inhomogeneities in the ferroelectric polarization over the smallest scales that can be observed, changes which are largely uncorrelated with topographic features. The application of an in-plane static electric field causes domain reorientation and domain wall motion over distances as small as 40 Å. These results demonstrate the utility of both CSOM and ANSOM in characterizing domain structure and dynamics in ferroelectric thin films.

Hysteresis

Scanning Probe Microscopy

10.1080/00150199908014814

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Citations (1)

AlSb/InAs HEMT's for low-voltage, high-speed applications

IEEE Transactions on Electron Devices (1998)

J.B. Boos W. Kruppa B. R. Bennett Daeui Park S. W. Kirchoefer

The design, fabrication, and characterization of 0.1 /spl mu/m AlSb/InAs HEMT's are reported. These devices have an In/sub 0.4/Al/sub 0.6/As/AlSb composite barrier above the InAs channel and a p/sup +/ GaSb layer within the AlSb buffer layer. The HEMT's exhibit a transconductance of 600 mS/mm and an f/sub T/ of 120 GHz at V/sub Ds/=0.6 V. An intrinsic f/sub T/ of 160 GHz is obtained after the gate bonding pad capacitance is removed from an equivalent circuit. The present HEMT's have a noise figure of 1 dB with 14 dB associated gain at 4 GHz and V/sub Ds/=0.4 V. Noise equivalent circuit simulation indicates that this noise figure is primarily limited by gate leakage current and that a noise figure of 0.3 dB at 4 GHz is achievable with expected technological improvements. HEMT's with a 0.5 /spl mu/m gate length on the same wafer exhibit a transconductance of 1 S/mm and an intrinsic f/sub T/L/sub g/, product of 50 GHz-/spl mu/m.

Transconductance

10.1109/16.711349

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Citations (139)

Strain tensor effects on SrTiO3 incipient ferroelectric phase transition

Journal of Electroceramics (2006)

Wontae Chang Jeffrey A. Bellotti S. W. Kirchoefer J.M. Pond

Infinitesimal strain theory

Strontium titanate

10.1007/s10832-006-9337-y

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Citations (15)

Directionally dependent ferroelectric phase transition order of anisotropic epitaxial BaxSr1−xTiO3 thin films

Applied Physics Letters (2006)

Jeffrey A. Bellotti Wontae Chang S. B. Qadri S. W. Kirchoefer J.M. Pond

Epitaxial Ba0.5Sr0.5TiO3 thin films were grown by pulsed-laser deposition on (100) LaAlO3 substrates in two distinct strain states, c∕a>1 and c∕a<1. X-ray diffraction measurements over the temperature range of 20°Cto−120°C showed that the change in the c∕a ratio with decreasing temperature was discontinuous and positive for the film with c∕a>1, and continuous and negative for the film with c∕a<1. These symmetry changes in the c∕a ratio with temperature were correlated with measurements of the in-plane dielectric properties, and showed that the polarization in these two types of structures has characteristically different behavior that is highly directionally-dependent.

Pulsed Laser Deposition

Transition temperature

Atmospheric temperature range

10.1063/1.2161937

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Citations (23)

The Effect of (Ba,Sr) and (Mn,Fe,W) Dopants on the Microwave Properties of Ba_xSr_1−xTiO₃ Thin Films

MRS Proceedings (1998)

Wontae Chang James S. Horwitz Won‐Jeong Kim J.M. Pond S. W. Kirchoefer

Pulsed Laser Deposition

10.1557/proc-541-699

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Citations (11)

Microstructure Evolution of Pulsed Laser‐Deposited (Ba, Sr)TiO₃ Films on MgO for Microwave Applications

International Journal of Applied Ceramic Technology (2005)

Sandwip K. Dey Prashant Majhi James S. Horwitz S. W. Kirchoefer W. J. Kim

To develop low‐loss tunable microwave circuits, based on the field dependence of dielectric permittivity, phase pure (Ba 0.5 , Sr 0.5 )TiO 3 doped with 1% W (BST) thin films 0.3‐μm thick were deposited on single crystal MgO wafers by pulsed laser deposition. The BST films were characterized by X‐ray θ–2θ scans and pole figure analysis, field emission scanning electron microscopy (FESEM), and cross‐sectional transmission electron microscopy (TEM), coupled with selected‐area electron diffraction (SAED). Although, the X‐ray θ–2θ scan indicated an epitaxial nature of BST with an out‐of‐plane orientation of (100), the pole figure analysis confirmed the presence (4–6%) of (111)‐oriented grains in a matrix of (100) textured grains. The columnar grains exhibited an in‐plane (i.e., along the plane perpendicular to the growth direction) grain size that was thickness‐dependent. The cross‐sectional TEM, coupled with SAED in the thickness direction, corroborated the pole figure analysis. Additionally, from X‐ray analysis, it was observed that the textured films were under in‐plane tension. The deposited film was characterized at microwave frequencies (1–20 GHz) using interdigitated electrodes deposited on top of the film. The film was characterized by a relatively low dielectric Q of 5–7. A 17% change in the capacitance was observed when applying a 40 V bias. From the observed microstructure, a preliminary understanding of its evolution and its relationship with the microwave dielectric properties is discussed, and some ideas to obtain truly epitaxial BST films are presented.

Selected area diffraction

Pulsed Laser Deposition

10.1111/j.1744-7402.2005.02003.x

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Citations (4)

Room-temperature ferroelectricity in strained SrTiO3

Nature (2004)

J. H. Haeni Patrick Irvin Wontae Chang R. Uecker P. Reiche

Strontium titanate

Transition temperature

10.1038/nature02773

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Citations (1,999)

Microwave amplification to 2.5 GHz in a quantum state transfer device

Applied Physics Letters (1985)

J.M. Pond S. W. Kirchoefer E. J. Cukauskas

Reflection amplification has been demonstrated from 40 MHz to 2.5 GHz using a bilevel superlattice structure known as a quantum state transfer device. Measurements of the magnitude and phase of the voltage reflection coefficient were made at 300 K using a specialized microwave probe. The maximum normalized gain, at 40 MHz, approaches the gain expected from dc measurements of the negative differential resistance.

Reflection coefficient

Reflection

10.1063/1.96317

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Citations (20)

Pulsed laser deposition of ferroelectric thin films for room temperature active microwave electronics

Integrated ferroelectrics (1997)

Adriaan C. Carter James S. Horwitz Douglas B. Chrisey J.M. Pond S. W. Kirchoefer

Abstract Single phase, (100) oriented Ba0.5Sr0.5TiO3 films have been deposited by pulsed laser deposition (PLD) onto (100) LaAlO3, SrTiO3, MgO substrates and single crystal (100) Ag films. Single phase, (100) oriented KTa0.6Nb0.4O3 films have been grown on (100) SrTiO3 and MgO. The dielectric properties of these films were measured as a function of DC bias at 1 MHz and 1 to 20 GHz. The 1 MHz measurements were made as a function of temperature between 30 – 350 K and the 1 to 20 GHz measurements were made at room temperature. Dielectric properties were measured using interdigitated and parallel plate capacitors. A 75% change in the capacitance was achieved using a 40 V bias across a 5 μm interdigitated capacitor gap (80 kV/cm). Capacitors with high tuning were always accompanied by low Q's (∼ 10's). Conversely, capacitor Q's in excess of 500 were observed but these films and poor tuning. Deposited films were annealed over a temperature range of 900 to 1250 C for 8 to 12 hours. Post annealing the films generally improved both the Q and percent tuning and indicates a direction for further dielectric film improvement.

Pulsed Laser Deposition

Film capacitor

Atmospheric temperature range

10.1080/10584589708013002

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Citations (37)