Grover Lamar Larkins

Florida International University | FIU · Department of Electrical and Computer Engineering

We have observed phenomena in phosphorus-doped graphene films consistent with mixed-state superconductivity at temperatures as high as 260 K. This evidence includes transport, susceptibility and Nernst/Hall measurements as a function of the thermal gradient. This paper presents evidence of vortices and flux flow in the mixed state of phosphorus-dop...

We have observed evidence of superconductivity at temperatures in the vicinity of 260 K in phosphorus-doped graphite and graphene. This evidence includes transport current, magnetic susceptibility, Hall effect and (pancake) vortex state measurements. All of these measurements indicate a transition which is that of a type II superconductor with no t...

A micro-electro-mechanical (MEM) switch built on a superconducting microstrip filter will be utilized to investigate BaTiO3 dielectric patches for functional switching points of contact. Actuation voltage resulting from the MEM switch provokes static friction between the bridge membrane and BaTiO3 insulation layer. The dielectric patch crystal stru...

We have observed periodically repeated steps in the resistance vs. temperature characteristics of doped Highly Oriented Pyrolytic Graphite and exfoliated doped multi-layer graphene. The observations consist of a series of regularly spaced steps in the resistance vs. temperature curves. The lowest step is observed at a temperature of from 50 to 60 K...

This work proposes to use capacitive micro-electro-mechanical systems (MEMS) switches built on a superconducting microstrip hairpin filter to investigate the reliability of MEMS for long term survivability. This device is made of a YBa₂Cu₃O₇ thin film deposited on a 20 mm × 20 mm LaAlO₃ substrate by pulse...

We have observed possible superconductivity using standard resistance versus temperature techniques in phosphorous ion implanted highly oriented pyrolytic graphite. The onset appears to be above 100 K and quenching by an applied magnetic field has been observed. The four initial boron implanted samples showed no signs of becoming superconductive wh...

Capacitively shunted microelectromechanical (MEM) switches were designed, fabricated and tested in an earlier work. The switch is composed of a coplanar waveguide (CPW) structure with an Au bridge membrane suspended above a center conductor covered with a BaTiO₃ dielectric. The membrane is actuated by electrostatic force acting between t...

High performance high Tc superconductor based series micro electromechanical system (MEMs) switches have been utilized to switch between a bandpass hairpin filter, center frequency f0=2.5GHz, and BW of 250MHz, and a through transmission line. This was accomplished with four switches actuated in pairs, one pair at a time. When the first pair is actu...

A superconductor circuit based on series Micro- Electro-Mechanical (MEM) switches is utilized to switch between two bandpass hairpin filters with 200 MHz bandwidth and nominal center frequencies of 2.1 GHz and 2.6 GHz. This is accomplished using 4 switches actuated in pairs, one pair at a time. When one pair is actuated the first bandpass filter is...

A summary of the current state of the art in MEM switches using high T C superconducting transmission line elements is presented. The most significant advantages of the MEM technology are the low mass and volume of the implemented devices. On the other hand one of the principal drawbacks of the room temperature MEM rf-switches are their losses. The...

In the fourth year of the project the work on optimization of fabrication process for a capacitively shunted RF micro-electromechanical superconducting switch was continued. Simulations and measurements show that the filter response is not critically distorted by the presence of the MEM switches. When the filter is not active, the signal is attenua...

We have successfully developed High Temperature Superconducting (HTS) MicroElectroMechanical (MEM) switches for RF applications. A typical switch is composed of a superconducting Yttrium Barium Copper Oxide (YBa₂Cu₃O₇) coplanar waveguide structure with a gold bridge membrane suspended above an area of the center con...

In earlier work a capacitively shunted superconducting MicroElectroMechanical (MEM) switch was designed and fabricated. The switch is composed of a superconducting YBa₂Cu₃O₇ coplanar waveguide structure with a Au bridge membrane suspended above an area of the center conductor covered with BaTiO₃ dielectri...

In earlier work a capacitively shunted superconducting MicroElectroMechanical (MEM) switch has been designed and fabricated. The switch is composed of high temperature superconducting (HTS) YBa₂Cu₃O₇ coplanar waveguide structure with a gold bridge membrane suspended above an area of the center conductor covered with...

In this work we have fabricated multiple MEM (micro-electro-mechanical) switches using a high-T_c superconductor to change the tap positions (open circuit termination to grounded termination) on a micro-strip "T"-resonator structure. MEM switches at different positions along the base of the "T's" resonator line introduce notches for diffe...

In this work an investigative study of the crystal structure of BaTiO3 thin films prepared using two techniques (laser ablation and RF magnetron sputtering) is presented. These films are to be used as the insulation layer in a capacitively shunted superconducting RF MEM switch with an insertion loss of better than 0.05 dB and an isolation of 30 dB...

The objective of this work is to fabricate, test and employ a high‐Tc superconductor based Micro‐Electro‐Mechanical (MEM) switch to change the tap position (open circuit termination to grounded termination) on a microstrip “T”‐resonator structure. Changing the tap position transforms the characteristic notches to bandpass for different operating f...

This work is an application of our high performance, high Tc superconducting Micro Electro-Mechanical (MEM) shunt switch to switch the resonance of a coplanar T-resonator structure. This structure (T resonator) was designed to operate at a resonant frequency of 4 GHz. Microwave switches based on MEM technology possess the advantages of small size,...

The objective of this work is to fabricate, test, and study a dielectrically loaded high temperature superconductor (HTS) spiral antenna that would operate in the frequency band of 10 MHz to 200 MHz. The antenna is formed by depositing and patterning a YBa2Cu3O7 (YBCO) thin film on top of 4-inch-diameter sapphire and Yittria Stabilized ZrO2 substra...

We have used a high performance (less than 0.05 dB insertion loss, greater than 30 dB isolation) high TC superconductor based MEM switch to insert a shunt microstrip resonator into a microstrip transmission line thus forming a ``T'' resonator structure. This allows the insertion of a series of notches and peaks (depending on termination of the shun...

We have used a high performance (less than 0.05 dB insertion loss, greater than 30 dB isolation) high-Tc superconductor based micro electromechanical (MEM) switch to insert a shunt microstrip resonator into a microstrip transmission line thus forming a 'T'-resonator structure. This allows the insertion of a series of notches and peaks (depending on...

We have designed, simulated and optimized a capacitively shunted RF MicroElectroMechanical (MEM) superconducting switch. The switch consists of a High Temperature Superconducting (HTS) YBa₂Cu₃O₇ coplanar waveguide (CPW) structure with a gold membrane bridge suspended above the center conductor and anchored at the gr...

We have developed a fabrication process for a superconducting MicroElectroMechanical (MEM) shunt switch. The design of the switch has been optimized using Sonnet simulations. The switch consists of a YBa₂Cu₃O₇ Coplanar Waveguide (CPW) transmission line with a gold membrane bridge anchored at the ground planes and su...

A high temperature superconducting microstrip line hairpin filter with BaTiO₃ has been designed and fabricated. The design and the filter simulation were done using Genesys software from Eagleware. In order to maximize the quality factor of the filter, the microstrip lines were made of superconducting YBa₂Cu₃O<sub>7...

Electronic noise has been investigated in Al _x Ga _1-x N / GaN modulation-doped field-effect transistors of submicron dimensions, grown by molecular beam epitaxy techniques. Some 20 devices were grown on a sapphire substrate. Conduction takes place in the quasi-two-dimensional (2D) layer of the junction (xy plane) which is perp...

We have fabricated microstrip hairpin bandpass filters using YBa2Cu3O7 and aluminum on LaAlO3. The insertion loss and bandwidth difference between the two identical (except for their conductor) devices has been used to estimate the unloaded Q of the aluminum resonators. The estimated unloaded Q of the aluminum resonators was 28. This is used to dis...

We have fabricated a three-pole microstrip hairpin bandpass filter using YBa2Cu3O7 on yittrium stabilized zirconia buffered (1 0 0) silicon. The corrected pass band insertion loss of the fabricated device was 7.76 dB and it's center frequency was 2.99 GHz with a bandwidth of 35.6 MHz. An identical device fabricated using aluminum on (1 0 0) Silicon...

For the purpose of comparison we have fabricated identical microstrip gap-coupled meanderline half-wave resonators using both 500 nm thick aluminum and 500 nm thick YBa2Cu3O7 high temperature superconductor films on 50 Ω cm (1 0 0) silicon buffered with a 50 nm film of yittria stabilized zirconia. The YBa2Cu3O7 films were crack-free and exhibited a...

We have fabricated microstrip gap-coupled meanderline half-wave resonators using 500 nm thick YBa2Cu3O7 high temperature superconductor films on 50 Ω⋅cm (100) silicon buffered with a nominally 50 nm thick film of yittria stabilized zirconia. The YBa2Cu3O7 films were crack-free and exhibited a zero resistance temperature of 82 K. Measured Q-values a...

We have fabricated a microstrip hairpin bandpass filter. In order to maximize the quality factor of the filter, the microstrip lines were made of superconducting YBa 2 Cu 3 O 7 . A thin layer of BaTiO 3 , patterned into patches, was deposited between the LaAlO 3 and the YBa 2 Cu 3 O 7 resonators. By varying the biasing acr...

We have made both patterned and unpatterned BaTiO 3 on YBa 2 Cu 3 O 7 microwave test structures as well as identical YBa 2 Cu 3 O 7 test structures and characterized them at 3.3 and 35 GHz. In both cases we found that the best unloaded Q values of the test resonators was for devices made from BaTiO 3 coated YBa 2 Cu 3 O 7 . This had led us to concl...

We have produced yttria-stabilized zirconia (YSZ) films on Si(100) for use as buffer layers for YBa2Cu3O7 microwave devices. The YSZ films, 30–100 nm thick, were grown by low frequency pulsed dc and rf magnetron sputtering under a variety of experimental conditions. YBa2Cu3O7 films, 300–600 nm thick, were grown using pulsed laser deposition in an a...

Scanning electron microscopy (SEM) has been utilized to study the microstructure of YBa₂Cu3O₇ superconductor high-temperature thin films under thermal cycling loading. The thin films were deposited on MgO buffered (100) Si substrates by the laser ablation and sputtering methods. It is found that the characteristics of the MgO...

The thermal cyclic behavior of the YBa₂Cu₃O ₇ high-temperature superconductor (HTS) thin film on Y-stabilized ZrO₂ buffered (100) Si was systematically studied in this paper. These HTS assemblies underwent thermal cycling from 77 K to room temperature, and their thermal fatigue reliability was evaluated b...

We have produced high quality superconducting half-wave microwave resonators on YBCO/YSZ/Si heterostructures. The YSZ was grown on (100) Si by pulsed dc magnetron sputtering at 820°C in 37 mTorr Ar/O₂. YBCO was then deposited on the YSZ/Si by pulsed laser ablation at 760°C in 0.5 Torr of O₂. A coplanar meander-line structure...

We have successfully fabricated high quality YBa₂Cu₃O₇ microwave “T” resonators on YSZ buffered P-type (100) oriented 53-56 ^Ω-cm silicon. The 40 to 50 nm thick yttria-stabilized zirconia buffer layer was deposited by pulsed dc magnetron sputtering at 830°C. The 250 to 400 nm thick YBa₂Cu<sub>3...

Current noise spectra were measured on low-ohmic TEGFETs (also called MODFETs or HEMTs), on nongated and gated devices. The spectra were measured with the three-point method, yielding S_I(ω), in the range 10 Hz to 1 MHz, and for temperatures of 78 to 295 K. Two to four Lorentzians were observed, which shifted to lower frequencies when the...

The focus of this work is to evaluate and compare Yttria Stabilized Zirconia (YSZ) thin films deposited on (100) silicon substrates, suitable for use as buffer layers for YBa2Cu3O7 (YBCO). The YSZ layers were grown using on-axis pulsed D.C. (PDC) and R.F. magnetron sputtering. After the buffer layer was grown, few samples were annealed at T≥900°C f...

Current noise spectra SI(ω) are reported on samples grown by the molecular beam epitaxy technique, with current-carrying contacts, acting as source and drain, and two probes extending into the two-dimensional electron gas (2DEG) of the AlGaAs/GaAs quantum well, in the range 77–295 K for frequencies of 10 Hz to 1 MHz. The time constants are almost i...

The use of MgO as a buffer layer between YBa₂Cu₃O₇ and Si has advantages for microwave applications. MgO has a low dielectric constant, small loss tangent and is relatively stable. Silicon as a substrate material is relatively inexpensive and, more importantly, active semiconductive devices can be imbedded in it. T...

We describe noise measurements in the frequency range 10 Hz-1 MHz on indium contacts to YBCO layers with a LaAlO/sub 3/ substrate. The spectra are of the 1/f/sup /spl alpha// type with /spl alpha/=1.2 above T/sub c/ and 1.15 below T/sub c/. Above T/sub c/ there is burst noise, although the averaged spectra are stable and reproducible, The voltage n...

We describe noise measurements in the frequency range 10 Hz-1 MHz on indium contacts to YBCO layers with a LaAlO3 substrate. The spectra are of the 1/f(alpha) type with alpha = 1.2 above T-c and 1.15 below T-c, Above T-c there is burst noise, although the averaged spectra are stable and reproducible. The voltage noise versus temperature, for a fixe...

Degradation studies of Bi-Sr-Ca-Cu-O (2223) superconducting ceramics were performed in N2, Ar2, O2, wet and dry air. By using a non-contact, room temperature technique the time dependence of the surface layer's impedance of Bi-Sr-Ca-Cu-O bulk ceramics is measured at 1 kHz in both dry and water vapour based environments.

We have observed shifts of from 0.5 to -6/spl deg/K in the T/sub C(ONSET/) of YBa/sub 2/Cu/sub 3/O/sub 7-x/(123) in laser ablated thin film 123-BaTiO/sub 3/ multilayer structures on (100) oriented LaAlO/sub 3/ upon poling of the BaTiO/sub 3/ with a positive potential. Poling was carried out at between 120 and 150/spl deg/C in air with an applied fi...

By energy resolved measurements of field electron emission, the gap of superconducting 2223 BiSrCaCuO was determined for the a-b direction of single-crystal specimens. The value of 2Delta(78 K)~50 meV is in agreement with results of other tunneling techniques.

The full-width-at-half-maximum, FWHM, of rare-gas (He, Ne) field ion energy distributions was measured in three different probe-hole FIMs, all combined with retarding potential analysis. The transmission functions of the spectrometers were analyzed through measurements of the total electron energy distributions. The FWHM resolution for ion energy s...

Low-frequency surface degradation studies of the YBa2Cu3O7-x (123) and Bi-Sr-Ca-Cu-O superconducting ceramics have been performed in N2, Ar2, O2, wet and dry air. The time dependence of the surface impedance of both 123 and Bi-Sr-Ca-Cu- O bulk ceramics are measured from 100 Hz to 20 kHz at room temperatures and pressures. In humid environments the...

Low-frequency surface degradation studies of the YBa2Cu3O7-x (123) and Bi-Sr-Ca-Cu-O superconducting ceramics have been performed in N2, Ar2, O2, wet and dry air. The time dependence of the surface impedance of both 123 and Bi-Sr-Ca-Cu- O bulk ceramics are measured from 100 Hz to 20 kHz at room temperatures and pressures. In humid environments the...

Surface degradation studies of the YBa₂Cu₃O _7-x (123) and Bi-Sr-Ca-Cu-O (2223) superconducting ceramics were performed in N₂, Ar₂, O₂, wet and dry air. By using a novel noncontact room-temperature technique the time dependence of the surface impedance of both 123 and Bi-Sr-Ca-Cu-O bu...

Different phases in the YO1.5-BaO-CuO phase diagram were evaluated for dielectric properties and compatibility with subsequent firing of a YBa2Cu3O7-x thick film. Y2BaCuO5 (211) was chosen for capacitor manufacture because it showed no reaction with the YBa2 Cu3O7-x (123) thick film upon sintering. AC field exclusion confirmed the superconductivity...

The time dependence of the surface impedance of YBa2Cu3O7−x (123) bulk ceramic superconductors was measured from 100 Hz to 20 kHz using a novel noncontact technique. The measurements were carried out at room temperature and in a variety of environments. All measurements were performed on freshly abraded 123 samples using a copper counter-electrode...

Different phases in the YO{sub 1.5}-BaO-CuO phase diagram were evaluated for dielectric properties and compatibility with subsequent firing of a YBaâCuâO{sub 7-x} thick film. YâBaCuOâ (211) was chosen for capacitor manufacture because it showed no reaction with the YBaâCuâO{sub 7-x} (123) thick film upon sintering. AC field exclusion confirmed that...

This paper reports on surface degradation studies of the YBaâCuâO{sub 7-x} (123) and Bi-Sr-Ca-Cu-O (2223) superconducting ceramics performed in Nâ, Arâ, Oâ, wet and dry air. By using a non-contact, room temperature technique the time dependence of the surface impedance of both 123 and Bi-Sr-Ca-Cu-O bulk ceramics are measured from 100 Hz to 20 kHz....

An array of integrated, n-channel, enhancement mode, field effect transitors using Langmuir-Blodgett films as gate insulators have been fabricated and studied.Effective insulator charge densities for the metal-Langmuir-semiconductor field effect transistors (MLSFETs) were found to be on the order of 1011q cm-2. The surface mobility of the MLSFETs w...

The use of a planar fabrication process in the semiconductor industry has been the single most important factor in the phenomenal growth of the complexity level of integrated circuits (ICs). We report herein the first insulated-gate field-effect transistors (IGFETs) with Langmuir-Blodgett (LB) gate insulators to be fabricated on silicon in a manner...

We report here the fabrication of Josephson junction tunnel diodes in which the barrier has been deposited using the Langmuir-Blodgett technique. Diodes have been fabricated using lead-indium alloys and niobium nitride for the electrodes. The barrier was vinyl stearate polymerized by Co⁶⁰γ radiation just prior to depositing the counter e...

We report the observation of the Josephson current in tunnel diodes in which the barrier is a monolayer of poly(vinyl stearate) deposited by the Langmuir-Blodgett technique. The fabrication of these diodes is described and the resulting current-voltage characteristic is given. A critical current density of 140 A cm−2 was obtained at 4.2 KK, the ene...

achieved was 1.2 % for 100 V of applied bias at 75 K. Results with this structure using SrTiO3 coupling capacitors resulted in a structure with no observable resonances, most probably due to extremely strong overcoupling (εr > 2,000) in the gap capacitances. The design, fabrication details and testing protocol are given in following sections of the...

Typescript. Department of Electrical Engineering and Applied Physics. Thesis (Ph. D.)--Case Western Reserve University.