Microwave Measurement of Dielectric Properties of Low-Loss Materials by the Dielectric Rod Resonator Method

Improvements both in accuracy and speed are described for the technique of measuring the microwave dielectric properties of low-loss materials by using a dielectric rod resonator short-circuited at both ends by two parallel conducting plates. A technique for measuring the effective surface resistance R/sub s/ of the conducting plates is proposed to allow the accurate measurement of the loss tangent tan delta. By means of the first-order approximation, the expressions are analytically derived for estimating the errors of the measured values of relative permittivity epsilon/sub r/, tan delta, and R/sub r/, for measuring the temperature coefficient of epsilon/sub r/, and for determining the required size of the conducting plates. Computer-aided measurements are realized by using these expressions. It is shown that the temperature dependence of R/sub s/, should be considered in the tan delta measurement. The copper plates used in this experiment have the relative conductivity of 91.0+-2.7 percent at 20°C, estimated from the measured R/sub s/ value. For a 99.9-percent alumina ceramic rod sample, the results measured at 7.69 GHz and 25°C show that epsilon/sub r/,= 9.687+-0.003 and tan delta = (1.6+-0.2)x 10/sup -5/. The temperature coefficients measured between 25 and 100°C are 112x10/sup -6//°C for epsilon/sub r/, and 23x10/sup -4//°C for tan delta.     

Temperature dependence of permittivity and loss tangent of lithium tantalate at microwave frequencies

Lithium tantalate (LiTaO/sub 3/) exhibits excellent electro-optical, piezoelectric, and pyroelectric properties and a very low thermal expansion. In this paper, we report measurements of loss tangent and the real part of the relative permittivity /spl epsiv//sub r/spl perp// measured in c-axis LiTaO/sub 3/ crystals in the temperature range from 14 K to 295 K at a frequency of 11.4 and 10 GHz. Microwave properties of LiTaO/sub 3/ were determined by measurements of the resonance frequency and the unloaded Q/sub o/ factor of a TE/sub 011/ mode cylindrical cavity containing the sample under test and accounting for uncalibrated cables and adaptors inside the cryocooler. The permittivity of LiTaO/sub 3/ was found to increase from 38.9 to 41.1 and the loss tangent to change from 1.1/spl times/10/sup -4/ to 6.5/spl times/10/sup -4/ over the full temperature range. Due to its low loss and relatively high permittivity, LiTaO/sub 3/ is suitable for microwave applications.     

Analysis and Evaluation of a Method of Measuring the Complex Permittivity and Permeability Microwave Insulators

Theory and experimental results are presented to show the possibility of using a resonant post technique for characterizing dielectric and magnetic materials at microwave frequencies. Results of the temperature dependence of the relative dielectric constant of nonmagnetic materials with /spl epsilon//sub r/, varying from 4 to 60 are presented and also loss tangent measurements at room temperature. The complex permittivity and permeability of a number of garnet materials has also been measured with 4/spl pi//spl gamma/M/sub s/ / /spl omega/ varying from 0.25 to 0.8. The measured real part of the permeability is in good agreement with the theoretical predictions of Schlomann and the imaginary part of the permeability agrees with measurements by Green et al. on similar materials.     

Voltage and frequency dependent dielectric properties of BST-0.5 thin films on alumina substrates

Dielectric properties of Ba/sub 0.5/Sr/sub 0.5/TiO/sub 3/ (BST-0.5) polycrystalline thin films, deposited on alumina substrates by means of reactive pulsed laser deposition (PLD), were measured at GHz frequencies using an interdigital capacitor (IDC). By applying a voltage up to 40 V between the two groups of fingers at room temperature, a high tunability of /spl sim/27% was achieved at 5 GHz. A relative dielectric constant of /spl sim/500 (consistent with the low-frequency IDC measurements) has been obtained using coplanar waveguides by means of the through-reflect-line (TRL) analysis combined with either a conformal mapping model or a full wave calculation. The BST loss tangent was estimated as /spl sim/0.05 in the range 3-16 GHz.     

Dissipative Parameters in Ferrites and Insertion Losses in Waveguide Y-Circulators Below Resonance

Extensive microwave loss measurements have been performed at frequencies from 1.3 to 11 GHz on below-resonance waveguide Y circulators loaded with a wide variety of ferrite and garnet compositions. Dissipative internal and external magnetic parameters have been measured on the same compositions. Also, dielectric loss measurements have been carried out. Two classes have been distinguished, defined by the following conditions: /spl omega//sub M/ / /spl omega/ /spl les/0.8 and 0.85 /spl les//spl omega//sub M/ / /spl omega/ /spl les/1.05. It is inferred that the (insertion loss) IL of such devices is independent of /spl Delta/H and mainly depends on the internal dissipative susceptibility x/sub i/" and on the dielectric loss tan /spl delta/. The relation of the IL versus x/sub i/" and tan /spl delta/ in the case /spl omega//sub M/ / /spl omega/ /spl les/0.8 is independent of frequency and given by the semiempirical equation IL= 10 log/sub 10/ (1-2.85 x/sub i/" - 1.60 tan /spl delta/ - 0.017)/sup -1/.     

A Highly Stabilized K/sub a/-Band Gunn Oscillator (Correspondence)

The construction and experimental results of a highly stabilized K/sub a/-band Gunn oscillator are described. The frequency stability is 3x10/sup -5/ at 25 GHz over the temperature range from 0 to 50/spl deg/C. An output power of more than 20 mW has been obtained in the frequency range up to 30 GHz. The frequency-saturation effect is also described.     

High temperature dielectric stability of liquid crystal polymer at mm-wave frequencies

The temperature dependent dielectric stability and transmission line losses of liquid crystal polymer (LCP) are determined from 11-105 GHz. Across this frequency range, LCP's temperature coefficient of dielectric constant, /spl tau//sub /spl epsi/r/, has an average value of -42 ppm//spl deg/C. At 11GHz the /spl tau//sub /spl epsi/r/ is the best (-3 ppm//spl deg/C), but this value degrades slightly with increasing frequency. This /spl tau//sub /spl epsi/r/ average value compares well with the better commercially available microwave substrates. In addition, it includes information for mm-wave frequencies whereas standard values for /spl tau//sub /spl epsi/r/ are usually only given at 10 GHz or below. Transmission line losses on 3- and 5-mil LCP substrates increase by approximately 20% at 75/spl deg/C and 50% or more at 125/spl deg/C. These insertion loss increases can be used as a design guide for LCP circuits expected to be exposed to elevated operating temperatures.     

Room temperature dual-mode oscillator-first results

An analysis is presented for a room temperature dual-mode oscillator (patent pending) utilising a single sapphire resonator in which two orthogonally polarised whispering gallery modes are excited. The temperature dependence of the 3.39 GHz beat frequency was aned near 304 K. An Allan deviation of 8/spl times/10/sup -12/ was measured at 1s.     

High-frequency modulation characteristics of 1.3-/spl mu/m InGaAs quantum dot lasers

In this letter, we report results of small-signal modulation characteristics of self-assembled 1.3-/spl mu/m InGaAs-GaAs quantum dot (QD) lasers at room temperature. The narrow ridge-waveguide lasers were fabricated with multistack InGaAs self-assembled QDs in active region. A high characteristic temperature of T/sub o/=210 K with threshold current density of 200A/cm/sup 2/ was obtained. Small-signal modulation bandwidth of f/sub -3 dB/=12 GHz was measured at 300 K with differential gain of dg/dn/spl cong/2.4/spl times/10/sup -14/ cm/sup 2/ from detailed characteristics. We observed that a limitation of modulation bandwidth in high current injection appeared with gain saturation. This property can direct future high-speed QD laser design.     

A low temperature dependent microstrip substrate

An X band resonant ring temperature coefficient and the coefficient of effective dielectric constant for a modified zirconate substrate have been measured as -1.58 × 10^-6per °C and 3.0 × 10^-6per °C over the temperature range -40°C to +120°C at X band. The effective dielectric constant at room temperature varies from 19.82 at 5.98 GHz to 21.24 at 11.61.     

RF, DC, and reliability characteristics of ALD HfO/sub 2/-Al/sub 2/O/sub 3/ laminate MIM capacitors for Si RF IC applications

High-performance metal-insulator-metal capacitors using atomic layer-deposited HfO/sub 2/-Al/sub 2/O/sub 3/ laminate are fabricated and characterized for RF and mixed-signal applications. The laminate capacitor can offer high capacitance density (12.8 fF//spl mu/m/sup 2/) up to 20 GHz, low leakage current of 4.9/spl times/10/sup -8/ A/cm/sup 2/ at 2 V and 125/spl deg/C, and small linear voltage coefficient of capacitance of 211 ppm/V at 1 MHz, which can easily satisfy RF capacitor requirements for year 2007 according to the International Technology Roadmap for Semiconductors. In addition, effects of constant voltage stress and temperature on leakage current and voltage linearity are comprehensively investigated, and dependences of quadratic voltage coefficient of capacitance (/spl alpha/) on frequency and thickness are also demonstrated. Meanwhile, the underlying mechanisms are also discussed.     

A K-Band Ruby Maser with 500-MHz Bandwidth (Short Papers)

Engineering improvements to a previously described reflected- wave maser design have resulted in an instantaneous 3-dB band-width of 400 MHz at 19.5 GHz, increasing to 560 MHz at 24 GHz. Nominal gain is 27 to 31dB and gain flatness is /spl plusmn/2.5 dB over this tuning range. Noise temperature variation across the passband is less than /spl plusmn/1.5 K and the effective noise temperature referred to the room temperature input flange ranges from 9.5/spl plusmn/4 K to 13.5/spl plusmn/4 K over the 18.5- to 25-GHz tuning range.     

High-speed Modulation of InGaAs: Sb-GaAs-GaAsP quantum-well vertical-cavity surface-emitting lasers with 1.27-/spl mu/m emission wavelength

1.27-/spl mu/m InGaAs: Sb-GaAs-GaAsP vertical-cavity surface-emitting lasers (VCSELs) were grown by metal-organic chemical vapor deposition and exhibited excellent performance and temperature stability. The threshold current changes from 1.8 to 1.1 mA and the slope efficiency falls less than /spl sim/35% as the temperature raised from room temperature to 70/spl deg/C. With a bias current of only 5 mA, the 3-dB modulation frequency response was measured to be 8.36 GHz, which is appropriate for 10-Gb/s operation. The maximal bandwidth is measured to be 10.7 GHz with modulation current efficiency factor (MCEF) of /spl sim/5.25 GHz/(mA)/sup 1/2/. These VCSELs also demonstrate high-speed modulation up to 10 Gb/s from 25/spl deg/C to 70/spl deg/C.     

A Highly Stabilized MIC Gunn Oscillator Using a Dielectric Resonator

An X-band frequency-stabilized MIC Gunn oscillator of a very simple structure using a dielectric resonator is developed. It is studied how the oscillating characteristics can be controlled by circuit parameters, with special attention to the factors affecting the frequency stability with temperature. By optimizing these factors and by selecting the proper temperature coefficient of a newly developed dielectric resonator, the high frequency stability of less than /spl plusmn/100 MHz over the temperature range from -20 to 60/spl deg/C (2x10 /sup -7/ / /spl deg/C) was obtained.     

Super-Schottky Mixer Performance at 92 GHz

As part of a program to explore the behavior of superconducting Schottky mixers at high frequencies (nu/sub RF//spl ges/90 GHz), the mixing and video performance of several super-Schottky diodes have been tested at 92 GHz. The diodes used (~3-mu m active diameter, doping concentration ~2x 10/sup 19/ cm/sup -3/) were identical to those recently developed at Aerospace for use in a 31-GHz mixer. The WR-10 mixer mount, designed specifically for this experiment, utilizes a quartz stripline assembly for the diode, whisker, and IF choke, suspended across quarter-height RF wavegnide. At 92 GHz, video responsivities were typically ~80 A/W (corrected for RF mismatch). Conversion loss(corrected for both RF and IF mismatches) was typically measured to he /spl gsim/18 dB. As expected, T/sub diode/ was small (< 5K). Video responsivity and conversion loss were also measured at an RF frequency of 3.95 GHz. These data were used with the measured I- V characteristics of the diodes to compare theoretical predictions of diode performance at 92 GHz in both the video and mixing modes, with the high-frequency data.     

A CMOS 0.25-/spl mu/m continuous-time FIR filter with 125 ps per tap delay as a fractionally spaced receiver equalizer for 1-gb/s data transmission

This paper presents a CMOS 0.25-/spl mu/m continuous-time 6-tap FIR filter that is used as a fractionally spaced receiver equalizer for 1-Gb/s data transmission. Each tap of the FIR filter delay line is realized with a second-order low-pass filter. Simulations show that the tap delay can be tuned from 100 ps to 300 ps while keeping a constant group delay within the bandwidth of 2.1 GHz and 800 MHz correspondingly. Experimental results show that the FIR filter can successfully recover a 1-Gb/s differential digital signal that has been transmitted over a 220-inch PCB trace which causes -31.48-dB attenuation at the symbol rate frequency of 1 GHz. The measured bit error rate after equalization is less than 10/sup -12/ over a 750-ps sampling range, compared to a 10/sup -2/ bit-error rate before equalization. Also presented are the measurement results comparing the horizontal and the vertical openings of the signals before and after equalization for PCB traces with different length. The chip dissipates 45 mW from a 2.5-V supply and occupies 0.33/spl times/0.27 mm/sup 2/ in a 0.25-/spl mu/m CMOS process.     

Frequency domain (1 kHz-40 GHz) characterisation of thin films for multichip module packaging technology

Parallel plate capacitors for the broadband dielectric characterisation of both high (amorphous BaTiO/sub 3/ and amorphous TaO/sub x/) and low (parylene) dielectric constant thin films were fabricated at low temperature (<200 degrees C). The dielectric constant and loss tangent were determined through the measurement of C, G and the S parameters of the capacitors. These thin film dielectrics exhibit no dispersion in the frequency range 1 kHz-40 GHz.<>     

High-density MIM capacitors using AlTaO/sub x/ dielectrics

The authors have obtained good MIM capacitor integrity of high-capacitance density of 10 fF//spl mu/m/sup 2/ using high-/spl kappa/ AlTaO/sub x/ fabricated at 400/spl deg/C. In addition, small voltage dependence of capacitance of <600 ppm (quadratic voltage coefficient of only 130 ppm/V/sup 2/) is obtained at 1 GHz using their mathematical derivation from measured high-frequency S parameters. These good results ensure the high-/spl kappa/ AlTaO/sub x/ MIM capacitor technology is useful for high-precision circuits operated at the RF frequency regime.     

Al/SiC carriers for microwave integrated circuits by a new technique of pressureless infiltration

Materials with high thermal conductivity and thermal expansion coefficient matching with that of Si or GaAs are being used for packaging high density microcircuits due to their ability of faster heat dissipation. Al/SiC is gaining wide acceptance as electronic packaging material due to the fact that its thermal expansion coefficient can be tailored to match with that of Si or GaAs by varying the Al:SiC ratio while maintaining the thermal conductivity more or less the same. In the present work, Al/SiC microwave integrated circuit (MIC) carriers have been fabricated by pressureless infiltration of Al-alloy into porous SiC preforms in air. This new technique provides a cheaper alternative to pressure infiltration or pressureless infiltration in nitrogen in producing Al/SiC composites for electronic packaging applications. Al-alloy/65vol% SiC composite exhibited a coefficient of thermal expansion of 7/spl times/10/sup -6/ K/sup -1/ (25/spl deg/C-100/spl deg/C) and a thermal conductivity of 147 Wm/sup -1/K/sup -1/ at 30/spl deg/C. The hysteresis observed in thermal expansion coefficient of the composite in the temperature range 100/spl deg/C-400/spl deg/C has been attributed to the presence of thermal residual stresses in the composite. Thermal diffusivity of the composite measured over the temperature range from 30/spl deg/C to 400/spl deg/C showed a 55% decrease in thermal diffusivity with temperature. Such a large decrease in thermal diffusivity with temperature could be due to the presence of micropores, microcracks, and decohesion of the Al/SiC interfaces in the microstructure (all formed during cooling from the processing temperature). The carrier showed satisfactory performance after integrating it into a MIC.     

High-performance MIM capacitor using ALD high-k HfO/sub 2/-Al/sub 2/O/sub 3/ laminate dielectrics

For the first time, we successfully fabricated and demonstrated high performance metal-insulator-metal (MIM) capacitors with HfO/sub 2/-Al/sub 2/O/sub 3/ laminate dielectric using atomic layer deposition (ALD) technique. Our data indicates that the laminate MIM capacitor can provide high capacitance density of 12.8 fF//spl mu/m/sup 2/ from 10 kHz up to 20 GHz, very low leakage current of 3.2 /spl times/ 10/sup -8/ A/cm/sup 2/ at 3.3 V, small linear voltage coefficient of capacitance of 240 ppm/V together with quadratic one of 1830 ppm/V/sup 2/, temperature coefficient of capacitance of 182 ppm//spl deg/C, and high breakdown field of /spl sim/6 MV/cm as well as promising reliability. As a result, the HfO/sub 2/-Al/sub 2/O/sub 3/ laminate is a very promising candidate for next generation MIM capacitor for radio frequency and mixed signal integrated circuit applications.