高温超导膜微波滤波器

我们用氧化锆单晶衬底GBCO高温超膜研制了超导膜悬微波低通滤波器。在77K测试获得:通带插损在0—2GHz,0—4GHz和0—6GHz通带内,分别为0.326dB,0.507dB和1.393dB。文中阐明悬置微带电路用于研制高介电常数衬底的高温超导微波无源器件是适宜的。     

SiGe pMODFETs on silicon-on-sapphire substrates with 116 GHzfmax

The dc and microwave results of Si_0.2Ge_0.8/Si_0.7Ge_0.3 pMODFETs grown on silicon-on-sapphire (SOS) substrates by ultrahigh vacuum chemical vapor deposition are reported. Devices with L_g=0.1 μm displayed high transconductance (377 mS/mm), low output conductance (25 mS/mm), and high gate-to-drain breakdown voltage (4 V). The dc current-voltage (I-V) characteristics were also nearly identical to those of control devices grown on bulk Si substrates. Microwave characterization of 0.1×50 μm² devices yielded unity current gain (f_T) and unilateral power gain (f _max) cutoff frequencies as high as 50 GHz and 116 GHz, respectively. Noise parameter characterization of 0.1×90 μm² devices revealed minimum noise figure (F_min) of 0.6 dB at 3 GHz and 2.5 dB at 20 GHz     

Comparison of Microwave Dielectric Properties of Ba0.6Sr0.4TiO3 Thin Films Grown on (100) LaAlO3 and (100) MgO Single-Crystal Substrates

The microwave properties of barium strontium titanate (Ba_0.6Sr_0.4TiO₃) thin films grown on (100) LaAlO₃ (LAO) and (100) MgO single-crystal substrates through the sol–gel technique were investigated. The interdigital capacitor (IDC) technique was used to measure the nonlinear dielectric properties in the frequency range from 1 GHz to 10 GHz. The results show that the Curie temperature, capacitance, and tunability of the films are strongly dependent upon the substrate. The film fabricated on the LaAlO₃ substrate has a higher tunability of 16.77% than that grown on the MgO substrate (～8.38%), measured at 10 GHz with an applied voltage of 35 V. The loss tangent is a linear function of the frequency in the microwave range, and the film grown on the MgO substrate has a lower loss tangent than that grown on the LAO substrate. This work reveals the great potential of Ba_0.6Sr_0.4TiO₃ (BST) films for application in tunable microwave devices.     

Dielectric constant, loss tangent, and surface resistance of PCB materials at K-band frequencies

This paper develops the theoretical approach and describes the design of a practical test rig for measuring the microwave parameters of unclad and laminated dielectric substrates. The test rig is based on a sapphire whispering-gallery resonator and allows the measurement of the following parameters: dielectric constant (epsiv) of the dielectric substrate in the range from 2 to 10, loss tangent (tandelta) of the dielectric substrate in the range from 10^-4 to 10^-2, and microwave losses of copper coating of the substrate in the range from 0.03 to 0.3 Omega. Measurements of numerous commonly used microwave printed-circuit-board materials were performed at frequencies between 30-40 GHz and over a temperature range of -50degC to +70degC     

High-isolation W-band MEMS switches

This paper presents the design, fabrication and measurement of single, T-match and π-match W-band high-isolation MEMS shunt switches on silicon substrates. The single and T-match design result in -20 dB isolation over the 80-110 GHz range with an insertion loss of 0.25±0.1 dB. The π-match design results in a reflection coefficient lower than -20 dB up to 100 GHz, and an isolation of -30 to -40 dB from 75 to 110 GHz (limited by leakage through the substrate). The associated insertion loss Is 0.4±0.1 dB at 90 GHz. To our knowledge, this is the first demonstration of high-performance MEMS switches at W-band frequencies     

Conductor-loss limited stripline resonator and filters

We report on stripline resonators on thin dielectric membranes that show dispersion-free, conductor-loss limited performance at 13.5 GHz, 27.3 GHz, and 39.6 GHz. The unloaded-Q (Q_u) of the resonators increases as √f with frequency and is measured to be 386 at 27 GHz. The measured results agree well with a new conformal mapping analysis. The stripline resonators are used in a micromachined state-of-the-art planar interdigitated bandpass filter at K-band frequencies. Excellent agreement has been achieved between the microwave model at 850 MHz and the 20 GHz filter. The micromachined filter exhibits a passband return loss better than -15 dB and a conductor-loss limited 1.7 dB port-to-port insertion loss (including input/output CPW line loss) at 20.3 GHz     

Low-Dielectric-Loss Barium Strontium Titanate Thin Films with MgO Buffer Layer for Tunable Microwave Devices

The dielectric and microwave properties of Ba_0.6Sr_0.4TiO₃ (BST60) thin films with a MgO buffer layer deposited on Al₂O₃ substrates were investigated. Insertion of the MgO buffer layer is demonstrated to be an effective approach to fabricate low-dielectric-loss BST thin films. x-Ray pattern analysis indicates that the thin films exhibit good crystalline quality with a pure perovskite phase and that insertion of the MgO buffer layer does not change the crystal structure of BST. The nonlinear dielectric properties of the BST films were measured by using an interdigital capacitor (IDC). At room temperature, the tunability of the BST films with a MgO buffer layer was 24.1% at a frequency of 1 MHz with an applied electric field of 80 kV/cm. The dielectric loss of the BST thin films is only 0.005 to 0.007 in the frequency range from 20 Hz to 2 MHz, the same as for BST films prepared on single-crystal MgO substrates. The microwave dielectric properties of the BST thin films were also measured by a vector network analyzer from 50 MHz to 10 GHz.     

High-temperature superconductor resonators and phase shifters

High-T_c resonators and hybrid digital phase shifters have been designed, fabricated, and tested. The YBa₂Cu₃O_7-δ (YBCO) films used were off-axis sputtered onto 0.5-mm-thick [100] LaAlO₃ substrates and have surface impedances at 10 GHz as low as 20 μΩ at 4.2 K and 300 μΩ at 77 K. The dielectric constant of the LaAlO₃ substrates was measured using straight-line and ring resonator techniques. The superconductor straight-line resonator, which uses silver as its ground plane, has a moderately high Q factor and has an electromagnetic feedthrough level below -65 dB up to 10 GHz. The authors also report the first demonstration of a semiconductor/superconductor microwave digital phase shifter. YBCO film was used to form the circuit, with semiconductor p-i-n diodes serving as switches. A 4-b superconductor phase-shifter design is also presented along with simulation results that indicate maximum total insertion loss (which occurs with all bits forward-biased) at 77 K to be 1.1 dB at 10 GHz     

The microwave properties of Li doped 0.7(Ba,Sr)TiO3-0.3MgO thick film interdigital capacitors on the alumina substrates

The crystalline and electrical properties of Li doped 0.7(Ba,Sr)TiO₃-0.3MgO thick film interdigital capacitors have been investigated. Screen printing method was employed to fabricate Li doped 0.7(Ba,Sr)TiO₃-0.3MgO thick films on the alumina substrates. (Ba,Sr)TiO₃ materials have high dielectric permittivity (>500 @ 1 MHz) and low loss tangent (0.01 @ 1 MHz) in the epitaxial thin film form. To improve dielectric properties and reduce sintering temperature, MgO and Li were added, respectively. 10 μm thick films were screen printed on the alumina substrates and then interdigital capacitors with seven fingers of 200 μm finger gap were patterned with Ag electrode. Current-voltage characteristics were analyzed with elevated temperature range. Up to 50 °C, the thick films showed positive temperature coefficient of resistivity (dρ/dT) of 6.11 × 10⁸ Ω cm/°C, then film showed negative temperature coefficient of resistivity (dρ/dT) of −1.74 × 10⁸ Ω cm/°C. From the microwave measurement, the relative dielectric permittivity of Li doped 0.7(Ba,Sr)TiO₃-0.3MgO thick films interdigital capacitors were between 313 at 1 GHz and 265 at 7 GHz.     

High-temperature superconductive devices on sapphire

The low-loss and uniform dielectric properties of sapphire make it attractive for high-performance microwave devices using high-temperature superconductors. YBa₂Cu₃O_7-δ films have been deposited on oxide-buffered 5-cm-diameter wafers and demonstrated a surface resistance of 0.5 mΩ at 10 GHz and 77 K. Long (9-ns) stripline delay lines have for the first time been produced on these substrates and have a measured insertion loss of 1.5 dB at 6 GHz and 77 K. Design techniques appropriate for the dielectric anisotropy of sapphire are discussed     

High-frequency, low-crosstalk modulator arrays based on FTC polymersystems

A novel electro-optic polymer Furan TetraCyano Indane (FTC) has been utilised in the fabrication of low V_π, high-speed travelling-wave Mach-Zehnder modulator arrays. The modulators were realised with microstrip transmission lines that were optimised resulting in a line loss of 3.64 dB/cm at 40 GHz. Mach-Zehnder modulators based on this design with 1.6 cm interaction length resulted in devices with V_π<5 V and a reasonably fiat frequency response up to 40 GHz. Electrical crosstalk measurements were also conducted on adjacent modulators separated by 400 μm in a modulator array. Without the implementation of any crosstalk reduction techniques, the measurement results indicated a crosstalk level of <-40 dB in the frequency band between 0 and 40 GHz. These impressive results were a consequence of the low dielectric constant of the polymer material at microwave frequencies and of the small lateral dimensions of the microstrip lines     

一种新型扇形环状频率选择表面的设计

通过在矩形环为基本单元结构的基础之上设计了一种新型双频双极化低通高阻型频率选择表面（Frequency Selective Surface,FSS）。此结构将普通矩形环的每条边顺时针延长,再沿贴片的四周开槽矩形孔径后两边加载介质板的多层结构,实现了Ka波段带通、W波段带阻的空间滤波特性。经过电磁仿真软件HFSS的仿真与优化,所设计的新型扇形环状FSS结构在35GHz谐振频率处,插损为0.02dB,-0.5dB通带衰减带宽为5.85GHz;在94GHz谐振频率处,反射系数为-54.57dB,-20dB阻带带宽为4.29GHz,且在入射角0°~30°范围内具有良好的极化稳定性和角度不敏感性。     

Artificial Dielectric Shields forIntegrated Transmission Lines

We present a novel shielding method for on-chip transmission lines built on conductive silicon substrates. The shield consists of an artificial dielectric with a very high in-plane dielectric constant, built from two patterned metal layers isolated by a very thin dielectric film. Inserted below an integrated coplanar transmission line, the artificial dielectric layer blocks the electric field of the line from entering the silicon substrate. Shielded coplanar waveguides fabricated on a conventional silicon wafer show a two- to three-fold loss reduction compared to unshielded lines at frequencies below 30 GHz.     

The influence of substrate properties on microwave losses in thin films of semiconductors

A method is presented for the contactless measurement at microwave frequencies of the resistivity of thin films of semiconductors deposited on insulating substrates. The resistivity is determined through a measurement of the change in the power loss or Q of a microwave cavity upon insertion of the sample. In addition to the intended application, knowledge can be obtained about microwave power losses in supported thin films. Calculated microwave losses in the semiconductor films are presented in a normalized form as a function of the thickness and electrical properties of both the film and the supporting substrate at 9.0 GHz (X band) and 23.0 GHz (K band). These calculations were made for germanium on calcium fluoride and sapphire substrates. The power losses are normalized on a unit surface area and a unit surface field intensity basis. Limited experimental data are presented for germanium on calcium fluoride. The computed curves show that a maximum in power dissipation for a fixed substrate thickness and frequency is reached at higher and higher film resistivities as the film thickness increases. A very strong dependence of power loss on substrate thickness is demonstrated.     

Long backfire antenna with insular image guide feed for dual frequency operation

A long backfire antenna using an insular image waveguide feed compatible with microwave dielectric integrated circuit technology is presented. The antenna operates as a backfire component from 9.7 to 9.9 GHz and as an endfire antenna from 8.9 to 9.9 GHz, with symmetrical radiation patterns and low crosspolarisation. The important parameters of the antenna are experimentally optimised to give a maximum gain of 20 dB and 17 dB when working as a backfire and endfire antenna, respectively. This type of antenna can find extensive applications at millimetre-wave frequencies.     

Asymmetrically Recessed 50-nm Gate-Length Metamorphic High Electron-Mobility Transistor With Enhanced Gain Performance

We report the design, fabrication and characterization of ultrahigh gain metamorphic high electron-mobility transistors. In this letter, a high-yield 50-nm T-gate process was successfully developed and applied to epitaxial layers containing high indium mole fraction InGaAs channels grown on GaAs substrates. A unique gate recess process was adopted to significantly increase device gain by effectively suppressing output conductance and feedback capacitance. Coupled with extremely small 10 mum times 25 mum via holes on substrates thinned to 1 mil, we achieved a 13.5 dB maximum stable gain (MSG) at 110 GHz for a 30-mum gate-width device. To our knowledge, this is the highest gain performance reported for microwave high electron-mobility transistor devices of similar gate periphery at this frequency, and equivalent circuit modeling indicates that this device will operate at frequencies beyond 300 GHz.     

AlGaN/GaN HEMTs on a (001)-Oriented Silicon Substrate Based on 100-nm SiN Recessed Gate Technology for Microwave Power Amplification

AlGaN/GaN high-electron mobility transistors on (001)-oriented silicon substrates with a 0.1-mum gamma-shaped gate length are fabricated. The gate technology is based on a silicon nitride (SiN) thin film and uses a digital etching technique to perform the recess through the SiN mask. An output current density of 420 mA/mm and an extrinsic transconductance g_m of 228 mS/mm are measured on 300-mum gate-periphery devices. An extrinsic cutoff frequency f_t of 28 GHz and a maximum oscillation frequency f_max of 46 GHz are deduced from S-parameter measurements. At 2.15 GHz, an output power density of 1 W/mm that is associated to a power-added efficiency of 17% and a linear gain of 24 dB are achieved at V_DS = 30 V and V_GS = -1.2 V.     

Dual-band bandpass tunable microwave photonic filter based on stimulated Brillouin scattering

A dual-band bandpass microwave photonic filter(MPF) based on stimulated Brillouin scattering(SBS) is theoretically analyzed and experimentally demonstrated. Two separated tunable laser sources(TLSs) are employed to generate two passbands by implementing phase modulation to amplitude modulation conversion by using SBS induced sideband amplification. The center frequencies of both passbands can be independently tuned ranging from 1 GHz to 19 GHz. High resolution with 3 d B bandwidth less than 30 MHz and large out-of-band rejection about 40 d B under 25 m W optical pump power are achieved.     

Distributed 2- and 3-bit W-band MEMS phase shifters on glass substrates

This paper presents state-of-the-art RF microelectromechanical (MEMS) phase shifters at 75-110 GHz based on the distributed microelectromechanical transmission-line (DMTL) concept. A 3-bit DMTL phase shifter, fabricated on a glass substrate using MEMS switches and coplanar-waveguide lines, results in an average loss of 2.7 dB at 78 GHz (0.9 dB/bit). The measured figure-of-merit performance is 93/spl deg//dB-100/spl deg//dB (equivalent to 0.9 dB/bit) of loss at 75-110 GHz. The associated phase error is /spl plusmn/3/spl deg/ (rms phase error is 1.56/spl deg/) and the reflection loss is below -10 dB over all eight states. A 2-bit phase shifter is also demonstrated with comparable performance to the 3-bit design. It is seen that the phase shifter can be accurately modeled using a combination of full-wave electromagnetic and microwave circuit analysis, thereby making the design quite easy up to 110 GHz. These results represent the best phase-shifter performance to date using any technology at W-band frequencies. Careful analysis indicates that the 75-110-GHz figure-of-merit performance becomes 150/spl deg//dB-200/spl deg//dB, and the 3-bit average insertion loss improves to 1.8-2.1 dB if the phase shifter is fabricated on quartz substrates.     

Low-loss on-chip transmission lines with micro-patterned artificial dielectric shields

Low-loss coplanar waveguide (CPW) transmission lines integrated on a standard (5 -10 Omega ldr cm) silicon substrate are realised by using an artificial dielectric shield with a very high in-plane dielectric constant. The shield consists of a 30 nm-thick Al₂O₃ film sandwiched by two 100 nm-thick aluminium layers patterned into lattices of mum-size elements. The individual metallic elements are micro-patterned to suppress the flow of eddy currents at microwave frequencies. Inserted below the CPW, the shield blocks the electric field of the line from entering the silicon substrate. The resulting line attenuation (measured up to 25 GHz) is comparable to that of identical CPWs built on a high-resistivity silicon wafer.