A Millimeter-Wave System-on-Package Technology Using a Thin-Film Substrate With a Flip-Chip Interconnection

In this paper, a system-on-package (SOP) technology using a thin-film substrate with a flip-chip interconnection has been developed for compact and high-performance millimeter-wave (mm-wave) modules. The thin-film substrate consists of Si-bumps, ground-bumps, and multilayer benzocyclobutene (BCB) films on a lossy silicon substrate. The lossy silicon substrate is not only a base plate of the thin-film substrate, but also suppresses the parasitic substrate mode excited in the thin-film substrate. Suppression of the substrate mode was verified with measurement results. The multilayer BCB films and the ground-bumps provide the thin-film substrate with high-performance integrated passives for the SOP capability. A broadband port terminator and a V-band broad-side coupler based on thin-film microstrip (TFMS) circuits were fabricated and characterized as mm-wave integrated passives. The Si-bumps dissipate the heat generated during the operation of flipped chips as well as provide mechanical support. The power dissipation capability of the Si-bumps was confirmed with an analysis of DC-IV characteristics of GaAs pseudomorphic high electron-mobility transistors (PHEMTs) and radio-frequency performances of a V-band power amplifier (PA). In addition, the flip-chip transition between a TFMS line on the thin-film substrate and a coplanar waveguide (CPW) line on a flipped chip was optimized with a compensation network, which consists of a high-impedance and low-impedance TFMS line and a removed ground technique. As an implementation example of the mm-wave SOP technology, a V-band power combining module (PCM) was developed on the thin-film substrate with the flip-chip interconnection. The V-band PCM incorporating two PAs with broadside couplers showed a combining efficiency higher than 78%.      

A V-Band Beam-Steering Antenna on a Thin-Film Substrate With a Flip-Chip Interconnection

We propose a planar V-band beam-steering antenna based on a millimeter-wave (mm-wave) system-on-package technology using advanced thin-film technology on a silicon mother board. The thin-film substrate has the capability of integrated passive elements and flip-chip interconnection. Space-consuming components such as a microstrip Rotman lens and patch antennas are implemented on a low-loss, low-cost, and low-dielectric-constant material, benzocyclobutane. V-band monolithic microwave integrated circuits, a power amplifier, and a SP4T switch, are flip-chipped on the thin-film substrate while minimizing parasitic effects. The fabricated antenna module shows if-plane beam steering at four angles, plusmn6deg and plusmn20deg. The measured effective isotropic radiated power is in the range of 17.3-18 dBm. To our knowledge, this is the first demonstration of a planar mm-wave beam-steering antenna module on a thin-film substrate incorporating integrated terminating loads and flip-chip interconnections.     

A novel surface-mountable millimeter-wave bandpass filter

A novel millimeter-wave waveguide bandpass filter structure suitable for surface mounting is introduced. The filter is constructed using a rectangular waveguide formed in MMIC substrate employing recently introduced microstrip-to-waveguide transducer. Input and output of the filter are implemented as microstrip lines. The transitions between the microstrip lines and the rectangular waveguide are implemented by using the microstrip-to-waveguide transition. The waveguide filter structure is surface-mountable as flip-chip and can be manufactured using a MMIC process that makes it extremely accurate. It has potential applications in millimeter-wave systems like local multipoint distribution system (LMDS) and autonomous cruise control (ACC) radar for automobiles     

Design of Millimeter Wave TFMS Bandpass Filter

In this paper, a Ka-band thin film microstrip line(TFMS) filter with multi-layer structure on silicon substrate is introduced. The simulated results show that it is possible to design compact millimeter-wave filter on silicon substrate with process compatible to current VLSI technology.     

A surface-mountable membrane supported filter

A silicon micro-machined filter with a simple planar integration on an other substrate is proposed in this article. The excitation is made from the top of the shielding substrate of a membrane supported micro-machined filter. Packaging and inter-connection are included in the design. Experimental results are presented on a two pole 30 GHz, 4% fractional bandwidth filter with a quality factor of 602 and insertion loss of 1.8 dB. Such a filter can be easily integrated in any circuit using flip-chip technology.     

Integration of 0/1-Level Packaged RF-MEMS Devices on MCM-D at Millimeter-Wave Frequencies

This paper reports on the development and optimization of 0/1-level packaged coplanar waveguide (CPW) lines and radio-frequency microelectromechanical systems (RF-MEMS) switches up to millimeter-wave frequencies. The 0-level package consists of an on-chip cavity obtained by flip-chip mounting a capping chip over the RF-MEMS device using BenzoCyclobutene (BCB) as the bonding and sealing material. The 0-level coplanar RF feedthroughs are implemented using BCB as the dielectric; gold stud-bumps and thermocompression are used for realizing the 1-level package. The 0-level packaged switches have been flip-chip mounted on a multilayer thin-film interconnect substrate using a high-resistivity Si carrier with embedded passives and substrate cavities. The insertion loss of a single 0/1-level transition is below -0.15 dB at 50 GHz. The measured return loss of a 0/1-level packaged 50-Omega CPW line remains better than -19 dB up to 71 GHz and better than -15 dB up to 90 GHz. It is shown that the leak rate of BCB sealed cavities depends on the BCB width, and leak rates as low as 10^-11 mbar.l/s are measured for large BCB widths (> 800 mum), dropping to 10^-8 mbar.l/s for BCB widths of around 100 mum. Depending on the bonding conditions, shear strengths as high as 150 MPa are achieved.     

Design of 50–70 GHz Planar Wideband Bandpass Filter on Liquid Crystal Polymer Substrate

In this paper, the authors propose a novel and compact 50-70 GHz planar microstrip bandpass filter, possessing sharp-rejection, low insertion-loss and wide-band characteristics, based on Liquid Crystal Polymer (LCP) substrates. The filter is fabricated on LCP substrates by using standard processing technologies. The proposed filter exhibits a return loss level better than 10 dB, an insertion loss of 5 dB and a 3-dB bandwidth of 30%.The measured and simulated results show good agreement, proving that LCPs are potential and very promising materials for flexible millimeter-wave substrate applications.     

Low-loss coplanar waveguides interconnects on low-resistivity silicon substrate

This paper describes fabrication, characterization and simulation of low-loss coplanar waveguide (CPW) interconnects on low-resistivity silicon substrate. The fabrication of CPWs is low-temperature (below 250/spl deg/C) and incorporates a spin-on low-k dielectric benzocyclobutene (BCB) and self-aligned electroplating of copper. The performance of CPWs is evaluated by high-frequency characterization and EM simulation. CPWs with different line width (W) and line spacing (S) are investigated and compared. Using a BCB layer as thick as 20 /spl mu/m, CPW fabricated on a low-resistivity silicon substrate exhibits an insertion loss of 3 dB/cm at 30 GHz.     

A highly integrated millimeter-wave active antenna array using BCB and silicon substrate

A simple and inexpensive packaging scheme is implemented in the design of an active antenna array module. The package consists of etched wells in a silicon wafer in which the components of the module are placed. A benzocyclobutene (BCB) film covers the components and serves as a substrate for interconnections. Prefabricated metallic bumps on the components are used for connection through the BCB film, eliminating the need for wire bonds. Aluminum coating of the silicon wafer isolates the lossy substrate from the millimeter-wave circuitry. This packaging process is applied to form an array of four cavity-backed patch antennas and then integrate it with a down-converter. The resulting active antenna array down-converts a 39-GHz received signal. The only off-wafer interconnects are for the 16-GHz local-oscillator input and a 7-GHz IF output. The effect of the packaging on the down-converter is described and important design features are noted. A detailed loss analysis is conducted based on measurements of the array performance.     

基于BCB的薄膜多层基板在毫米波T/R组件中的应用

基于BCB的薄膜多层基板具有优异的高频特性,是毫米波频段多芯片组件集成封装的重要途径。研究了BCB薄膜多层基板在Ka波段相控阵雷达T/R组件中应用的可行性,首先与LTCC基板对比验证了BCB微带线的传输特性,然后研制了功率分配/合成器、穿墙过渡等关键微波无源电路,最后设计了八通道的无源组件进行微波性能测试评估,结果表明基于BCB的薄膜多层基板能够满足应用需要。     

A uniplanar compact photonic-bandgap (UC-PBG) structure and itsapplications for microwave circuit

This paper presents a novel photonic bandgap (PBG) structure for microwave integrated circuits. This new PBG structure is a two-dimensional square lattice with each element consisting of a metal pad and four connecting branches. Experimental results of a microstrip on a substrate with the PEG ground plane displays a broad stopband, as predicted by finite-difference time-domain simulations. Due to the slow-wave effect generated by this unique structure, the period of the PBG lattice is only 0.1λ₀ at the cutoff frequency, resulting in the most compact PEG lattice ever achieved. In the passband, the measured slow-wave factor (β/k₀) is 1.2-2.4 times higher and insertion loss is at the same level compared to a conventional 50-Ω line. This uniplanar compact PBG (UC-PBG) structure can be built using standard planar fabrication techniques without any modification. Several application examples have also been demonstrated, including a nonleaky conductor-backed coplanar waveguide and a compact spurious-free bandpass filter. This UC-PBG structure should find wide applications for high-performance and compact circuit components in microwave and millimeter-wave integrated circuits     

Millimeter-wave silicon MMIC interconnect and coupler usingmultilayer polyimide technology

This paper reports our latest progress in developing low-loss and low-crosstalk silicon MMIC interconnects for millimeter-wave applications. The proposed silicon/metal/polyimide (SIMPOL) structure based on multilayer polyimide technology is extremely effective in reducing noise crosstalk, and also provides very low line loss, even at the millimeter-wave regime. The measurement results of the developed SIMPOL structures demonstrate extremely low noise crosstalk (<-40 dB) in the entire frequency range (up to 50 GHz), which is limited by the dynamic range of the measurement equipment, and excellent insertion loss (<-0,25 dB/mm) up to 45 GHz. In addition, the SIMPOL concept is applied for the first time successfully in the design and fabrication of branch-line hybrids at millimeter-wave frequencies, 30 and 37 GHz     

Benzocyclobutene as Substrate Material for Planar Millimeter-Wave Structures: Dielectric Characterization and Application

The application of benzocyclobutene (BCB) polymer as dielectric substrate material for millimeter-wave microstrip structures is investigated in this paper to face the problem of large losses due to standard dielectrics in the high microwave range. Dielectric properties of BCB are characterized from S-parameter measurements on a conductor-backed coplanar waveguide (CBCPW) using the polymer as substrate material. Excellent features, with a low loss tangent and a stable dielectric constant, are demonstrated within the measurement range from 11 GHz to 65 GHz. As a validation of BCB high frequency performances, the design and experimental characterization of a V-band array on BCB substrate is presented. Measurement results on both matching and radiation characteristics of the millimeter-wave array are discussed.     

Novel low-cost planar probes with broadside apertures for nondestructive dielectric measurement of biological materials at microwave frequencies

Novel planar-type probes were developed to demonstrate the possibility of replacing the existing high-cost open-ended coaxial probes. The planar probes of this study define an aperture on the broadside of the probe body. In this way, the contact area can be maximized and/or customized according to specific medical needs. The probes with various aperture sizes and shapes can also be fabricated simultaneously in a single batch process. Three probes are developed in this paper: a probe combining two laminates, a microelectromechanical systems (MEMS)-based probe with a single benzocyclobutene (BCB) layer on a quartz substrate, and another MEMS probe with two BCB layers defined on a silicon substrate. The third probe was specifically designed for monolithic integration with driving circuits on a single substrate. Limitations in the high-frequency performance of the planar probes were carefully studied, and higher order modes and incomplete shielding were found to be the main causes. The measurement results of each probe showed excellent compatibility with those of the open-ended coaxial probe up to almost 40 GHz. The proposed planar-type probes have great potentials for practical medical applications in view of low cost, disposability, and monolithic integration capability with the driving circuits.     

低耗低剖面单层波导阵列天线研究

新型单层波导阵列天线具有低耗、低剖面、结构紧凑、实用性强等诸多优点, 在毫米波甚至太赫兹无线通信领域具有巨大应用潜力, 是当前的研究热点。 文章首先介绍了用于构建波导阵列天线的几类波导馈电网络的特点, 指出E 面波导馈电网络在毫米波应用领域的优势,接着针对E 面波导在单层并馈波导阵列天线和Butler矩阵多波束阵列天线方面的研究展开叙述,最后给出了可应用在单层波导阵列天线中的开口波导辐射单元在实现多频和圆极化等不同功能上的最新研究进展。 文章对于低耗低剖面单层波导阵列天线的发展及其应用具有参考价值。     

低损耗衬底上实现无源低通滤波器

分析比较了不同种类衬底上无源器件(片上电感和电容)的损耗机理,在OPS(氧化多孔硅)和HR(高阻硅)低损耗衬底上分别实现了片上低通滤波器.为了研究衬底损耗,设计了平面螺旋电感,其Q值在两种衬底上的仿真结果都超过了20.在OPS衬底上的低通滤波器实测-3dB带宽为2.9GHz,通带插入损耗在500MHz为0.87dB;在HR衬底上的低通滤波器实测-3dB带宽为2.3GHz,通带插入损耗在500MHz为0.42dB.     

低损耗衬底上实现无源低通滤波器

分析比较了不同种类衬底上无源器件(片上电感和电容)的损耗机理,在OPS(氧化多孔硅)和HR(高阻硅)低损耗衬底上分别实现了片上低通滤波器.为了研究衬底损耗,设计了平面螺旋电感,其Q值在两种衬底上的仿真结果都超过了20.在OPS衬底上的低通滤波器实测-3dB带宽为2.9GHz,通带插入损耗在500MHz为0.87dB;在HR衬底上的低通滤波器实测-3dB带宽为2.3GHz,通带插入损耗在500MHz为0.42dB.     

The flip-chip bump interconnection for millimeter-wave GaAs MMIC

The flip-chip bump interconnection structure has become popular for microwave and millimeter-wave package applications. This structure is expected to provide higher performance and a low cost packaging method. This paper presents the results of an evaluation of flip-chip assembled radio frequency (RF) devices. A coplaner transmission line type GaAs monolithic microwave integrated circuit (MMIC) was mounted on an aluminum oxide (Al₂O₃) substrate using the flip-chip thermal compression method. The electrical performance (S-parameter and noise figure) was measured and the reliability of the interconnection was tested. The changing rate of the characteristic impedance (Zo) of transmission line on bare-chip caused by bare-chip surface proximity to a substrate was simulated by finite element method (FEM) analysis. Flip-chip bonding conditions were fixed to keep the gap that less than 1% of Zo changing rate and sufficient bonding strength for reliability of interconnection. The DC characteristics of a 30 GHz, 60 GHz and 77 GHz band low noise amplifier (LNA) were the same before and after mounting, and the RF performance of the assembled MMIC was the same as the bare-chip without packaging. However, the influence of underfilling was observed. When epoxy resin was injected into the gap between the bare-chip and the substrate, the frequency band of the MMIC shifted to the low side. The reliability of the bump interconnection was excellent. The interconnection resistance did not change in a temperature cycle (-55°C to +125°C until 1500 cycle) test     

A W-Band Air-Cavity Filter Integrated on a Thin-Film Substrate

In this letter, a W-band air-cavity filter has been developed on a thin-film substrate using a lossy silicon substrate as a base plate, which is suitable for a mm-wave system-on-package. The lossy silicon suppresses a parasitic substrate mode excited in a thin-film substrate, while a coupling loss between a transmission line and a resonator is minimized by etching the backside of the lossy silicon substrate underneath the coupling area. In the backside etching process, 70 mum of silicon was left for mechanical support of the thin-film substrate. The resonator was fabricated using a low-cost silicon micromachining technique and was flip-chip integrated on a thin-film substrate. The fabricated air-cavity resonator showed an unloaded Q of 851 at a resonant frequency of 94.18 GHz. Improvement in the coupling loss by the backside etching process was verified with measurement results. The fabricated filter exhibited an insertion loss of 1.75 dB and a return loss better than 14.5 dB with a 1.3% 3 dB fractional bandwidth at a center frequency of 93.8 GHz.     

Negative refraction in a Si-polymer photonic Crystal membrane

We have observed negative refraction in a photonic crystal (PC) membrane structure at near-infrared wavelengths. The device is fabricated on a silicon-on-insulator substrate and consists of a silicon rod matrix suspended in a polymer where optical energy is delivered by ridge waveguides with various incident angles. The propagation direction inside the PC shows extraordinary refraction with an angle consistent with our two-dimensional numerical simulations. To our knowledge, this is the first experimental observation of isotropic negative refraction in a Si-based planar PC structure at optical frequencies. The realization of negative refraction in a planar Si-based system enables applications in negative index imaging to be integrated into compact optical circuits.