Silicon high-resistivity-substrate millimeter-wave technology

The application of molecular beam epitaxy (MBE) and X-ray lithography for the fabrication of monolithic integrated millimeter-wave devices on high-resistivity silicon has been investigated. Process compatibility and the retention of high-resistivity characteristics were measured using the spreading resistance method and Hall measurements after various process steps. Microstrip resonators of ring and linear geometry were fabricated on 10 000 Ω.cm silicon substrates. For linear microstrip resonators, the attenuation was found to be less than 0.6 dB/cm at 90 GHz. A 95-GHz IMPATT oscillator circuit and a planar microstrip antenna array have been fabricated on highly insulating silicon substrates. For the oscillator, a combined monolithic-hybrid integration technique was used to attach the discrete IMPATT diode to the resonator circuit. The oscillator does not require tuning elements. Preliminary experimental results are 8 mW of output power with 0.2 percent efficiency at 95 GHz.     

A novel fabrication process of MEMS devices on polyimide flexible substrates

Micro-electro-mechanic-system (MEMS) devices on flexible substrate are important for non-planar and non-rigid surface applications. In this paper, a novel and cost-effective fabrication process for an 8 × 8 MEMS temperature sensor array with a lateral dimension of 2.5 mm × 5.5 mm on a polyimide flexible substrate is developed. A 40 μm thick polyimide substrate is formed on a rigid silicon wafer using as a mechanical carrier throughout the fabrication by four successive spin coating liquid polyimide. The arrayed temperature sensing elements made of 1200 Å sputtered platinum thin film on polyimide substrate show excellent linearity with a temperature coefficient of resistance of 0.0028/°C. The purposed sensor obtains a high sensitivity of 0.781 Ω/°C at 8 mA at constant drive current. Because of the low heat capacity and excellent thermal isolation, the temperature sensing element shows excellent high sensitivity and a fast thermal response. The finished devices are flexible enough to be folded and twisted achieving any desired shape and form. Employing spin-coated liquid polyimide substrate instead of solid polyimide sheet minimizes the thermal cycling as well as improves the production yield. This fabrication technique first introduces the spin-coated PDMS (Polydimethylsiloxane) interlayer between the silicon carrier and the polyimide substrate and makes the polyimide-based devices separate much easier and greatly simplifies the fabrication process with a high production yield. A non-successive two-stage cure procedure for the polyimide precursor is developed to meet low-temperature requirement of the PDMS interlayer. The fabrication procedure developed in this research is compatible with conventional MEMS technology through an optimized integration process. The novel flexible MEMS technology can benefit the development of other new flexible polyimide-based devices.     

Ion-implanted planar-mesa IMPATT diodes for millimeter wavelengths

A process has been developed that combines ion-implantation doping with planar and mesa-etching techniques for the fabrication of fully passivated millimeter-wave IMPATT diodes. The device geometry consists of an IMPATT diode surrounded by a two-layer annular region of passivation: one layer of high-resistivity semiconductor and the other of thick insulator material. Devices constructed with this new geometry have sufficient mechanical strength to allow direct mounting into microwave circuits without the use of an insulator standoff and metal ribbon package arrangement. A simple model of the diode-circuit interaction is used to estimate the degradation in microwave performance as a function of the passivation parasitics. These results are compared to a diode with no parasitic losses. Based on the I²-PLASA process, a fully passivated silicon IMPATT diode was fabricated for V-band (50-75-GHz) operation. Degradation factors of approximately 50 percent are predicted for the present devices. A continuous-wave output power of 100 mW was obtained at 62 GHz from an I²-PLASA IMPATT diode with an implanted p⁺-n-n⁺doping profile. Mechanical tuning characteristics of these devices were found to be more broad-band than standard packaged diodes. The measured AM and FM noise spectra close to the carrier were representative of standard single-drift silicon millimeter-wave IMPATT diodes.     

Dielectric Resonator Antenna on Silicon Substrate for System On-Chip Applications

This paper presents for the first time the design and performance of a novel integrated dielectric resonator antenna fabricated on a high conducting silicon substrate for system on-chip applications. A differential launcher to excite the ${rm TE}_{01delta}$ mode of the high permittivity cylindrical dielectric resonator was fabricated using the IBM SiGeHP5 process. The proposed antenna integrated on a silicon substrate of conductivity 7.41 S/m has an impedance bandwidth of 2725 MHz at 27.78 GHz, while the achieved gain and radiation efficiency are 1 dBi and 45% respectively. The design parameters were optimized employing Ansoft HFSS simulation software. Very good agreement has been observed between simulation and experimental results. The results demonstrate that integration of dielectric resonator antennas on silicon is viable, leading to the fabrication of high efficient RF circuits, ultra miniaturization of ICs and for the possible integration of active devices.      

Air-gap polycrystalline silicon thin-film transistors for fully integrated sensors

Air gap thin-film transistors (TFTs) were fabricated using a solid phase crystallization process. Undoped polycrystalline silicon (polysilicon) was used as the active layer and a highly doped polysilicon bridge was used as the gate, which promotes the air gap. These TFTs have comparable threshold voltage (V/sub T/) and subthreshold slope characteristics to TFTs fabricated using pulsed laser crystallization, and using silicon dioxide as gate insulator. The low value of V/sub T/ is very important for low power consumption. Moreover, the air-gap TFT fabrication process is compatible with low-temperature glass substrate technology, which allows the integration of sensors and electronics 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     

Substrate transfer for RF technologies

The constant pressure on performance improvement in RF processes is aimed at higher frequencies, less power consumption, and a higher integration level of high quality passives with digital active devices. Although excellent for the fabrication of active devices, it is the silicon substrate as a carrier that is blocking breakthroughs. Since all devices on a silicon wafer have a capacitive coupling to the resistive substrate, this results in a dissipation of RF energy, poor quality passives, cross-talk, and injection of thermal noise. We have developed a low-cost wafer-scale post-processing technology for transferring circuits, fabricated with standard IC processing, to an alternative substrate, e.g., glass. This technique comprises the gluing of a fully processed wafer, top down, to an alternative carrier followed by either partial or complete removal of the original silicon substrate. This effectively removes the drawbacks of silicon as a circuit carrier and enables the integration of high-quality passive components and eliminates cross-talk between circuit parts. A considerable development effort has brought this technology to a production-ready level of maturity. Batch-to-batch production equipment is now available and the technology and know-how are being licensed. In this paper, we present four examples to demonstrate the versatility of substrate transfer for RF applications.     

Polysilicon thin-film transistors on polymer substrates

Different approaches to fabricate low-temperature polycrystalline silicon (LTPS) thin film transistors (TFTs) on polymer substrates are reviewed and the two main routes are discussed: (1) standard fabrication of LTPS TFTs on glass substrates followed by a transfer process of the devices on the polymeric substrate; (2) direct fabrication of the devices on the polymeric substrate. Among the different techniques we have described in more detail the process we have recently developed for the fabrication of LTPS TFTs directly on ultra-thin polyimide (PI) substrate. LTPS TFT technology is particularly suited for high performance flexible electronics applications, due to the excellent device characteristics, good electrical stability and CMOS technology. Flexible display application remains the most attractive application for LTPS technology, especially for AMOLED displays, where device stability and the possibility to integrate the driving circuits make LTPS technology superior to all the other competitive TFT technologies. Among the other applications, particularly promising is also the application to flexible smart sensors, where integration of a front-end electronics is essential. Some examples of flexible gas sensors and pressure sensors, integrated with simple readout electronics based on LTPS TFTs and fabricated on ultra-thin PI substrate, are presented.     

How to make an ideal HBT and sell it too

New technology of active packaging (AP) is proposed. It permits the implementation of device structures that require lithography on opposite sides of a thin semiconductor crystal layer. A major goal of the AP technology is to integrate III-V devices with silicon integrated circuitry on a single substrate; the purpose, however, is not only to “teach the old dog new tricks” but also to greatly expand the assortment of tricks available. The concept is illustrated by describing a process for the fabrication of a collector-up InP heterojunction bipolar transistor, capable of oscillation in the frequency range of 300-400 GHz. An attractive application for this technology is the implementation of millimeter and submillimeter phased antenna arrays, in which beam steering is accomplished by amplitude modulation of array elements at a fixed phase difference. Focal plane antenna arrays on a silicon chip should have important applications in automobile collision avoidance and early warning systems, as well as satellite communication systems     

3-D Integration of 10-GHz Filter and CMOS Receiver Front-End

A 10-GHz filter/receiver module is implemented in a novel 3-D integration technique suitable for RF and microwave circuits. The receiver designed and fabricated in a commercial 0.18-mum CMOS process is integrated with embedded passive components fabricated on a high-resistivity Si substrate using a recently developed self-aligned wafer-level integration technology. Integration with the filter is achieved through bonding a high-Q evanescent-mode cavity filter onto the silicon wafer using screen printable conductive epoxy. With adjustment of the input matching of the receiver integrated circuit by the embedded passives fabricated on the Si substrate, the return loss, conversion gain, and noise figure of the front-end receiver are improved. At RF frequency of 10.3 GHz and with an IF frequency of 50 MHz, the integrated front-end system achieves a conversion gain of 19 dB, and an overall noise figure of 10 dB. A fully integrated filter/receiver on an Si substrate that operates at microwave frequencies is demonstrated.     

Status and trends of silicon RF technology

The current research and development activities in silicon radio-frequency (RF) technologies are first reviewed, accompanied by an illustration of the most pronounced shortcomings of conventional silicon technology in the integrability of RF functions at high GHz frequencies. In the discussion on active RF devices mainly CMOS is investigated due to great interest in this mass-production technology. Issues related to the integration of spiral inductors on silicon are addressed, stressing in particular the difficulty of RF substrate potential definition. Silicon micromachining techniques are highlighted as potential solutions to the integration of RF passives and to reduce substrate losses and cross-talk on silicon. It is explained that micromachining techniques are the best introduced to the silicon mainstream by using post-processing and minimum process complexity.     

系统集成中的高阻硅IPD技术

集成无源器件(IPD)技术可以将分立的无源器件集成在衬底内部,提高器件Q值及系统集成度。由于高阻硅衬底具有良好的射频特性,高阻硅IPD技术可以制备出Q值高达70以上的电感。高阻硅IPD基于薄膜技术具有高精度、高集成度等特点,可将无源器件特征尺寸缩小一个数量级。同时可利用成熟的硅工艺平台,便于批量生产降低成本。此外,高阻硅IPD技术可与硅通孔(TSV)技术兼容,可实现三维叠层封装。分析表明,高阻硅IPD技术在系统集成中具有广泛应用前景。     

CMOS on FZ-high resistivity substrate for monolithic integration ofSiGe-RF-circuitry and readout electronics

The choice of a highly resistive substrate for silicon millimeter-wave integrated circuits (SIMMWIC) imposed by the requirement of low RF-substrate losses requires the adaptation of a CMOS process on float zone silicon (FZ). A comparison of n- and p-channel devices realized on high resistivity substrate (p-type, 5000 Ω·cm) and standard CMOS substrates (CZ, n-type, 4-6 Ω·cm) is given. Using careful process design, we obtained device characteristics on FZ-substrates that are closely similar to those on standard material, thus allowing direct transfer of existing circuit designs     

LCP基板在微波/毫米波系统封装的应用

液晶聚合物(LCP)在微波/毫米波频段内介电常数低,损耗小,并且其热稳定性高、机械强度大、吸湿率低,是一种适合于微波/毫米波电路应用、综合性能优异的聚合物材料。LCP基板可实现无源、有源器件的埋置和集成,且具有一定的气密特性,是一种具备实现系统级封装(SOP)能力的基板技术。文章系统地介绍了基于LCP材料基板的性能,并分析了相对于传统聚四氟乙烯(PTFE)基板的优势。还综述了近年来LCP基板作为微波/毫米波系统封装的研究进展,并指出LCP基板是一种具有良好发展前景的微波/毫米波系统级封装技术路线。     

Integrated packaging of over 100 GHz bandwidthuni-traveling-carrier photodiodes

Hybrid packaging techniques, in which the device substrate is different from the package substrate, and wire bonding or solder interconnections are used, are inadequate for ultrahigh-speed (>100 GHz) wideband applications. By employing wafer-bonding techniques, an integrated packaging (IP) technology was developed, in which devices are fabricated directly on the package substrate, and the interconnections are made as a part of the device fabrication process. This IP process was used to fabricate uni-traveling-carrier photodiodes (UTC-PD's) integrated with millimeter-wave coplanar waveguides (CPW) on package compatible sapphire with high yield. The performance of wafer-bonded UTC-PD's with 3-dB bandwidth of 102 GHz was similar to that of conventional devices, and the CPW's exhibited low dispersion     

A 31-GHz monolithic GaAs mixer/preamplifier circuit for receiver applications

The portion of a monolithic receiver containing integrated Schottky mixer diodes and MESFET'S with microstrip circuitry has been developed and tested at 31 GHz. This work is part of a program to establish the feasibility of monolithic receivers and transmitters at microwave and millimeter-wave frequencies. Receiver designs using high-cutoff frequency diodes in a mixer configuration followed by a MESFET amplifier are capable of operating from microwave through millimeter-wave frequencies. However, the fabrication of monolithic receiver designs requires the integration on the same wafer of devices with different material requirements. We have developed a compatible integration scheme which is fundamental to the fabrication of monolithic receivers at millimeter-wave frequencies. Fabrication and design considerations for the 31-GHz balanced mixer and IF preamplifier are described. Completed monolithic units typically exhibit a conversion gain of 4 dB from the signal frequency of 31 GHz to the IF frequency of 2 GHz. The associated noise figure is typically 11.5 dB.     

Micromachined devices for wireless communications

An overview of recent progress in the research and development of micromachined devices for use in wireless communication subsystems is presented. Among the specific devices described are tunable micromachined capacitors, integrated high-Q inductors, micromachined low-loss microwave and millimeter-wave filters, low-loss micromechanical switches, microscale vibrating mechanical resonators with Q's in the tens of thousands, and miniature antennas for millimeter-wave applications. Specific applications are reviewed for each of these components with emphasis on methods for miniaturization and performance enhancement of existing and further wireless transceivers     

Planar millimeter-wave antennas using SiNx-membranes onGaAs

Planar aperture coupled microstrip antennas for 77 GHz are demonstrated for the first time. As far as possible standard GaAs monolithic microwave/millimeter-wave integrated circuit (MMIC) technology is used to realize the antennas. The antenna patches are suspended on a thin dielectric SiN_x membrane on GaAs substrate. Therefore a novel plasma-enhanced chemical vapor deposition (PECVD) process step for the fabrication of the membranes is developed and described. The single antenna patches are coupled to a microstrip line through an aperture in the ground metallization. The method of moments in spectral domain is applied to design the patches. The feed network of a 3×1 antenna array for homogeneous excitation is simulated and optimized with a microwave design system (MDS). From reflection measurements the operation frequency of this triple patch antenna is determined to be 77.6 GHz. The farfield antenna characteristics are measured in an anechoic chamber, showing good agreement between simulated and measured results and a co- to cross-polarization isolation better than 30 dB     

A Si bipolar 28-GHz dynamic frequency divider

A dynamic frequency divider applying the regenerative frequency division principle has been developed. A spiral inductor on the silicon substrate used as a load is characterized, and an improved one-port model with the substrate resistance is discussed. A 1/16 frequency divider was implemented with a silicon bipolar technology with a cutoff frequency of 40 GHz. The operation frequency range was 11.8-28.1 GHz, covering the Ka band (18-26.5 GHz). The inductive load has improved the maximum operation frequency by 7%, compared with a conventional circuit. Complemented with a 21-GHz static frequency divider previously reported by the authors, the whole microwave frequency range up to 26.5 GHz has been completely covered with the silicon bipolar technology. The maximum operation frequency of a silicon MMIC has been extended to the millimeter-wave frequency region for the first time