hybrid ferroelectric/ superconducting microwave...

Hybrid Ferroelectric/Superconducting Microwave Circuits

Robert R. RomanofskyNASA Glenn Research Center

Cleveland, OH

Recent progress in processing and deposition techniques along with bettermodeling and novel circuit designs have resulted in thin film ferroelectric-superconductorand ferroelectric-metal components that rival the microwave performance of state-of-the-art counterparts. Not long ago a coupled microstripline phase shifter patterned on aYBa2Cu3O7-δ/SrTiO3/LaAlO3 multilayer structure exhibited more than 400 degrees ofcontiguous phase shift with less than 5 dB of insertion loss at Ku-band when cooled to 77K. A figure of merit around 100o/dB was ultimately achieved. Similar devices wereconstructed using BaxSr1-xTiO3 films and metal electrodes for room temperatureoperation. The best figure of merit thus far is about 70 o/dB. It is unclear what rolesurface effects from different electrodes play in determining performance.

Attempts to reduce the high loss tangent of these thin films (compared to singlecrystals) have included annealing and the use of dopants. With Ba1-xSrxTiO3 films atroom temperature annealing seemed to have little effect in terms of the tunability to lossratio of K-band phase shifters. However, closer to the Curie temperature there are verydefinite effects at low (i.e. MHz) frequencies. Annealing appears to increase themaximum dielectric constant by about a factor of 2, and also increases the tanδ to a lesserextent. The largest values of phase shift per insertion loss have been obtained from 1%Mn doped laser ablated films grown by the Naval Research Laboratory. As opposed toDRAM applications, for microwave circuits relatively thick films are required. The so-called “dead-layers” at ferroelectric interfaces may explain why some researchers havereported much lower values for peak dielectric constant than we routinely see withmicrowave devices. Besides thickness, film crystallinity directly influences tunability.But we consistently observe degradation in film crystallinity with increasing thickness.An accurate theoretical model of the ferroelectric coupled line phase shifters based on avariational solution for line capacitance and well-known coupled line theory has beendeveloped. The role of film thickness is examined.

Besides phase shifters a Ku-band voltage controlled oscillator based on a 3λ ringresonator patterned over a 2 µm thick SrTiO3 film demonstrated a ≈5 % tuning range at40 K. Other components that are under development include tunable bandpass filtersintended for cryogenic operation and tunable microstrip patch antennas. A prototype 16-element phased array radar, based on BaxSr1-xTiO3 films, for potential automotivecollision warning applications will also be discussed. And, finally, a design for a newtype of scanning phased array antenna called the “ferroelectric reflectaray” will bepresented.

Outline

• Background: Applications of High Tc Superconductivity and Ferroelectric Films to Satellite & Terrestrial Communications• Coupled Microstrip Phase Shifters Using Au and YBa2Cu3O7-δ Electrodes on SrTiO3 and BaxSr1-xTiO3 Films• A Theoretical Approach Based on a Variational Formulation of Line Capacitance• Tunable Resonators and Voltage Controlled Oscillators• Materials Issues: Reliability, Uniformity, and Cost• The Prospect of Phased Array Antennas Based on Ferroelectric Technology

Lewis Research Center

Approach

Potential Enterprise Benefits

Features

Direct Data Distribution (D3)

A Pathfinder for Commercial Communications Insertion

• 19 GHz MMIC TransmitPhased Array

– LeRC/RaytheonCooperativeAgreement with 50/50cost sharing

• Hitchhike Experiment on Shuttlefor NASA missions risk mitigationand commercial servicesdemonstration

• Commercially ownedand operated spaceand groundsegments atcommercialfrequency

• Direct distribution of spacedata from LEO at 622 Mbpsto end user or archivefacility via terrestrialnetworks

• Cryoreceiver-based 0.9 mTracking Earth Terminal

– LeRC integration of InPPHEMT LNA, HTS filter,and cryocoolertechnologies

• Off-load TDRSS for– Latency tolerant data delivery from

LEO S/C– Communications outage restoration

• Commercial service providers reduce cost

• 155 Mbps Multi-channelDigital Encoder-Modulator

– LeRC/SICOM SBIR IIand Space ActAgreement

D3

Direct Data Distribution 1.ppt

JSC


Cryoreceiver

• A cryoreceiver is baselined for theD3 Earth terminal - Allows smallerdiameter reflector (0.9 m instead of1.8 m) with wider beam width,simplifying tracking

CassegrainReflector

OrthomodeCoupler

• Low Thermal Loss Waveguides

• 1 W Cryocooler

Cold Finger

• Vacuum Can

• Low Sidelobe Feed Horn

• HTS Filter

• Cryogenically cooled receiver will achieve a noise temperature of ~ 150º K, a factor of ~ 4reduction at 19 GHz, improving receiver performance by a factor of 4 (6db)

• 6db is very highly significant to communication system designers - Enables a smallerspace (or Earth) antenna... or increased data rate... or lower power....

Features• Exploits three key

technologies:– Reliable cryocooler– HTS Filter– InP PHEMT low noise

receiver (LNA) chip

• Other design features:– Vacuum can with low

thermal loss waveguides– Low sidelobe feed horn

• InP LNA (PHEMT)

To Down Convertors

For further information: Contact Robert Romanofsky (216)-433-3507

Lewis Research CenterX-Band Cryoreceiver

Space Qualified X-band Hybrid Superconductor/Semiconductor Receiver[Cooperative development by NASA Lewis Research Center and the Jet PropulsionLaboratory for High Temperature Superconductor Space Experiment (HTSSE);delivered to NRL in 1994]

Cryogenic S-Parameter Characterization Station


On-Wafer Cryogenic Probe Station

Wyw

Odd mode

E-field

h0>>(h1+h2), H1<<h2W>>(2w+s)

s

X

xGround plane

Y1

Y2

h0

h1

h2

0

1

2

Cross-Sectional View of Ferroelectric Coupled Microstripline Phase Shifter

Ferroelectric Phase Shifter

FerroelectricPhase Shifter

Element (1 of 4)

Barium StrontiumTitanate (0.3 micron -optically transparent)

Radial StubBias Tee

180 degrees totalphase shift at 400volts bias

V+

GRD

Magnesium OxideSubstrate (500 micron -optically transparent)

CETDP ProductCETDP Product

Gold - 2 micron

1 cm

Photograph of Four Element CoupledMicrostripline Phase Shifter

0.0

-4.0

–8.0

–12.0

–16.0

S 21

(dB

)

0V

25V

50V

100V 150V

Measured Insertion Loss (including SMA launchers) of an 8-element ≈50 Ω PLD coupled microstripline phase shifter at 290 K as a function of bias voltage. Substrate is 0.3 µm MgO with 400 nm Ba0.60Sr0.40TiO3 film. l = 350 µm, s = 7.5 µm and w = 30 µm. Bandwidth compression from the filtering effect is evident. Marker 1, 2, 3, and 4 are at –5.75, -5.38, -6.00, and –6.49 dB, respectively.

High Voltage “Bias Tee” for Ferroelectric Circuits

Fail-safe bias tee allows voltages of up to 500 V to be applied to ferroelectric devices and circuits connected to expensive and delicate microwave instrumentation

Measured insertion loss of packaged “bias-tee”

8-section 50 Ohm coupled microstrip phase shifter at 40 K using YBa2Cu3O7-δ electrodes and laser ablated SrTiO3 films on (100) single crystal 0.25 mm LaAlO3. Hysteresis is unremarkable. l = 470 µm, s = 7.5 µm, and w = 25µm.

Inse

rtio

n P

has

e (d

eg)

Insertio

n lo

ss (dB

)

Performance of 8-section coupled line thin ferroelectric film phase shifters from different vendors


Performance Comparison of Various PLD Samples.

8 element CMPS using the 305 µm thick MgO design also employing BST mesassample Substrate BST film thick fopt

GHzTuning w/400V

Max Loss(dB)

Max K(°/dB)

UM 112 MgO 60:40 400 23.5 280° 6.5 43UM 142 MgO 60:40 400 23.5 276° 11.5 24

4 element CMPS using the 305 µm thick MgO design, 1% Mn doped films with no mesassample Substrate BST film thick fopt

GHzTuning w/400V

Max Loss(dB)

Max K(°/dB)

NRL 98111001 MgO 60:40 am-a 350 18 137.0° (160V) 5.614 24.4NRL 98111002 MgO 60:40 am-a 500 18.5 121.9° 1.991 61.2NRL 98111201 MgO 60:40 am-a 750 20 88.6° 0.875 101.3NRL 98111201 MgO 60:40 am-a 750 20.06 80.8° 1.437 56.2

8 element CMPS using the 254 µm thick LaAlO3 designsample Substrate BST film thick fopt

GHzTuning w/400V

Max Loss(dB)

Max K(°/dB)

UM NBST001 LaAlO3 50:50 350 14.3 201° 4.6 43.7UM NBST017 LaAlO3 50:50 700 15 223° (360 V) 6.43 34.7SCT B111497B LaAlO3 40:60 750 14 271° 7.01 42.7


Experimental Comparison of SrTiO3 Film Thickness Effects for a 25 Ω CoupledMicrostrip Phase Shifter on 0.25 mm LaAlO3

•Data from SrTiO3 films showed that phase shift increased almost linearly

with film thickness, actually closer to ∆ϕ ~ t 0.67 in agreement with models

•If ferroelectric phase shift/loss is constant, then thicker films will yield better performance: lower overall loss since conductor loss is constant & more compact

A Simple Example of a “Variational” Solution to a Partial Differential Equation

∂2φ/∂x2 + ∂2φ/∂y2 + ρ/ε = 0 (1)

Given the boundary conditions: φ(a,y)=φ(-a,y)=φ(x,b)=φ(x,-b) = 0 (2)

Assume a solution: φ(x,y) = (a2-x2)(b2-y2)(k1 +k2x2 +k3x

4 + …) (3)

Implying that the “x” dimension is >> “y”

δφ =(a2 – x2)(b2 – y2)δk1 (4)

where δφ is the first small variation in φ.

Variational form of equation 1 for a one-term solution:

Substituting (4) into this expression:

k1 = 5/8(ρ/ε)(1/(a2 + b2))

The final solution is:

φ(x,y) = 5/8 (1 – (x/a)2)(1 – (y/b)2)(1 + (b/a)2)-1[(ρ/ε)b2]

403020Frequency (GHz)

100

Pha

se (d

egre

es) 100

0

–100

40302010Frequency (GHz)

0

Ret

urn

loss

or

inse

rtio

n lo

ss (d

B)

–10

0

–20

–30

–40

S21S11 εr = 500

εr = 3500

Theoretical calculation for the bandpass characteristic of an 8-section coupled microstripline phase shifter using a 0.5 m BaxSr1–xTiO3 film on 0.3 mm thick MgO. The coupled length was 350 m, w = 30 m, ands = 10 m. The permittivity of the film was tuned from 3500–j0.05 (no bias) to 500–j0.005 (maximum bias).


Comparison of the Quasi-TEM Solution and an E-M simulator for the Case of Microstrip

Table 1. Data for a 2 micron ferroelectric layer on .25 mm thick LaAlO3,Zo∼50 Ohms, s>>w,h (micro mode)

Er Ferroelectric Layer Eeff (Sonnet) Eeff (Variational)300 18.76 18.43600 21.34 21.00900 23.49 23.091200 25.41 24.931500 27.18 26.591800 28.84 28.12

The model is useful for a wide variety of multilayer transmission lines. In this case,the strip spacing (s) was allowed to increase just until the even and odd mode capacitancebecame equal (Zoo=Zoe).

3 λλ 25 ΩΩ Au/SrTiO3/LaAlO3 Tunable Ring Resonator


• First demonstration ofa cryogenic tunableoscillator using bothGaAs PHEMT andthin film ferroelectrictechnologies thatoperates in themicrowave frequencyrange.

Electronically Tunable K-Band Oscillator


Cryogenic GaAs PHEMT/Ferroelectric Ku-Band Tunable Oscillator

A Side-Coupled Au/SrTiO3 3λλ Ring Resonator Provided Over 500 MHz Tuning at Ku-Band. The Laser Ablated Ferroelectric Film was 2 µµm Thick. Bias was between 0 and 250 V.


BER Degradation Due To Phase Noise and Q

PhaseNoisedBC/Hz

(After Leeson)

Un-coded QPSK

Comparison of the Resistivity of an Evaporated Thin Gold Film and Bulk Gold and Implications for Device Design

+ 1 µm Au∆ Bulk Au

T, K

ρ(T), Ωcm

Gold Phase Shifter Skin Effect

00.20.40.60.8

11.21.41.6

18 19 20 21 22

Frequency (GHz)

0.5

1

2.5

5

Measured resistivity of evaporatedgold on alumina

Effect of film thickness on the insertion loss of a single section coupled microstrip BaxSr1-xTiO3 phase shifter using thin film resistivity values

Extracting λL(0) from Strip Resonators

Correction factor as a function of reduced temperature for a Tl-Ba-Ca-Cu-O thin film (800 nm)≈50 Ω ring resonator on 500 µm LaAlO3. The normalized resonant frequency shifts because ofthe temperature dependent impedance and coupled susceptance.

Circuit model of a [superconducting] transmission line near resonance coupled to a [superconducting] feed line

Modeled Effect of YBa2Cu3O7-δ Penetration Depth and Film Thickness

Insertion loss and return loss of a 6-poleYBa2Cu3O7-δ microstrip band-pass filter on 0.30 mm MgO with t=200 nm andλo=200 nm

Insertion loss and return loss of a 6-poleYBa2Cu3O7-δ microstrip band-pass filter on 0.30 mm MgO with t=200 nm andλo=300 nm


Life Cycle Testing of BaxSr1-xTiO3 Devices

Fig. 2. Transmission S-parameter (S21) insertion loss versus voltage cycle for a Au/BSTO(0.75 µm)/MgO(300 µm), four-element CMPS at 18 GHz and 300 K. Ba:Sr ratio is 60:40.

Fig. 3. Transmission S-parameter (S21) phase shift (degrees) versus voltage cycle for a Au/BSTO(0.75µm)/MgO (300 µm), four-element CMPS at 18 GHz and 300 K. Ba:Sr ratio is 60:40.


Insertion Loss and Phase Shift of a 4-Section Coupled MicrostripPhase Shifter on High Resistivity Si at 298 K

An ultimate goal is to integrate superconducting or metallic transmission lines and electrodes with crystallineferroelectric films on silicon to enable more complicated microelectronic circuits and to reduce manufacturing costs.The epitaxial heterostructures described here were very tunable and exhibited low loss and may lead to exciting new devices. The fundamental structural similarities between cuprate superconductors and perovskite ferroelectricsencourages such development. The large difference in lattice constant and thermal expansion coefficient between these materials and silicon appears to be a tractable problem.


Cross Sectional TEM of a heterostructure consisting of 80 nm (ZrO2)0.91(Y2O3)0.09/200 nmBi4Ti3O12/375 nm Ba 0.6Sr0.4TiO3 films on 100 Si

A thin interfacial layer is present at the YSZ-BTO interface. The BTO-BSTO interface appears abrupt.

Prototype 16-Element Linear Phased Array Antenna Based onBa0.60Sr0.40TiO3 Thin Films

Measured Principal Plane Boresight Patterns of the 16 ElementPhased Array at 23.7 GHz

-100

-90

-80

-70

-60

-50

-40

-30

-20

-10

0

-100 -90 -80 -70 -60 -50 -40 -30 -20 -10 0 10 20 30 40 50 60 70 80 90 100

Angle from Boresight [Degrees]

No

rmal

ized

Am

plit

ud

e [d

B]

E-plane (co-polar)

H-plane (co-polar)

16-Element Ferroelectric Phased Array Controller

Lewis Research Center Reflectarray Prototype

19.4” diameter

• Printed CP Element with integrated• Ferroelectric FilmPhase Shifter

Subarray

Characteristics

• 2832 elements - 17616-element subarrays

• 3 dB insertion loss perphase shifter

• 39 dBi gain at 19 GHz

Patent Pending

Acknowledgements

NASA Glenn Research Center:Sam AlterovitzFelix MirandaCarl MuellerFred Van KeulsJoe Warner

University of MarylandChadwick CanedyRammamoorthy Ramesh

Naval Research LaboratoryJim Horwitz

MicroCoating TechnologiesGeorge CuiJerry Schmitt

Wen-Yi Lin

hybrid ferroelectric/ superconducting microwave...

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