MEMS Switched Tunable Inductors

This paper presents a new implementation of integrated tunable inductors using mutual inductances activated by micromechanical switches. To achieve a large tuning range and a high quality factor, silver was used as the structural material, and silicon was selectively removed from the backside of the substrate. Using this method, a maximum tuning of 47% at 6 GHz is achieved for a 1.1 nH silver inductor fabricated on a low-loss polymer membrane. The effect of the quality factor on the tuning characteristic of the inductor is investigated by comparing the measured result of identical inductors fabricated on various substrates. To maintain the quality factor of the silver inductor, the device was encapsulated using a low-cost wafer-level polymer packaging technique.     

Chip-level integration of RF MEMS on-chip inductors using UV-LIGA technique

This paper presents a chip-level integration of radio-frequency (RF) microelectromechanical systems (MEMS) air-suspended circular spiral on-chip inductors onto MOSIS RF circuit chips of LNA and VCO using a multi-layer UV-LIGA technique including SU-8 UV lithography and copper electroplating. A high frequency simulation package, HFSS, was used to determine the layout of MEMS on-chip inductors with inductance values close to the target inductance values required for the RF circuit chips within the range of 10%. All MEMS on-chip inductors were successfully fabricated using a contrast enhancement method for 50 μm air suspension without any physical deformations. High frequency measurement and modeling of the integrated inductors revealed relatively high quality factors over 10 and self-resonant frequencies more than 15 GHz for a 1.44 nH source inductor and a 3.14 nH drain inductor on low resistivity silicon substrates (0.014 Ω cm). The post-IC integration of RF MEMS on-chip inductors onto RF circuit chips at a chip scale using a multi-layer UV-LIGA technique along with high frequency measurement and modeling demonstrated in this work will open up new avenues with the wider integration feasibility of MEMS on-chip inductors in RF applications for cost-effective prototype applications in small laboratories and businesses.     

Surface micromachined high-performance RF MEMS inductors

High-performance three-dimensional (3-D) microinductors with air-core and polyimide-core were fabricated by using simple MEMS technology. Both inductors have electroplated copper coils to minimize resistance to obtain high quality factor. The measurement results show that both inductors have high Q-factors over wide range of operating frequency. The maximum Q-factor of the polyimide-core is 36.5 and the inductance is 1.42 nH at 4.5 GHz, while the maximum Q-factor of the air-core inductor is 22.9 and the inductance is 1.17 nH at 5.5 GHz. The series resistance/parasitic capacitance of the polyimide-core inductor and air-core inductor is 1.05 Ω/1.07 pF and 1.82 Ω/0.57 pF respectively at the peak-Q frequency.     

Design, fabrication and testing of sandwich coupled inductors

A planar coupled inductor having sandwich coil structure is fabricated using MEMS microfabrication techniques. The structure of the inductor coil is designed to achieve high coupling and high winding number with a relatively small coil area. In this work, the structure is fabricated by bonding two planar on-chip coil fabricated on two different substrates. This method can replace the conventional via connections that cause various problems in output pads interconnection. The functionality of the fabricated device was tested, while the basic characteristics of the fabricated coil were measured at wide range of operating frequency using cascade GSG probe and compared with the simulation. For measurements up to 1?GHz, three resonance frequencies, inductance of 35?nH and resistance of as low as 25?Ω were observed. The results show that the proposed technique is a promising alternative method for fabricating a simple and cost effective 3-D coupled inductors.     

High performance suspended spiral inductor and band-pass filter by wafer level packaging technology

Suspended inductors and 2.45 GHz BPF with patterned ground shields on the lossy silicon substrate by using Cu/BCB based wafer level packaging and bulk Si etching technologies were fabricated. Thick BCB interlayer is used as the supporting dielectric and the backside cavity is easily removed by using a two-step back-etching process. The fabricated 2.7 nH inductor has a maximum Q factor 49 at 8.2 GHz and high Q factors more than 22 in the broadband frequency range from 1 to 10 GHz. And the realized 2.45 GHz BPF has the insertion loss of 3.0 dB and the return loss of more than 14 dB at the pass band. It is also featured by more than 48 and 25 dB attenuation at 0.9 and 1.8 GHz respectively, with the second harmonic rejection being 33 dB.

     

Design and fabrication of the suspended high-Q spiral inductors with X-beams

In this paper, deep sub-micron CMOS process compatible high Q on-chip spiral inductors with air gap structure were designed and fabricated. In the design the electromagnetic solver, SONNET, and the finite element program, ANSYS, were used for electrical-characteristics and maximum mechanical strength, respectively. The copper wires were capped with electroless Ni plating to prevent the copper from oxidizing. A Si₃N₄/SiO₂ X-beam was designed to increase the mechanical strength of the inductor in air gap. The enhancement of maximum mechanical strength of a spiral inductor with X-beams is more than 4,500 times. Among these structures, the measured maximum quality factor (Q) of the suspending inductor and frequency at maximum Q are improved from 5.2 and 1.6 GHz of conventional spiral inductor to 7.3 and 2.1 GHz, respectively.     

Polymer-core conductor approaches for RF MEMS

In many radio frequency (RF) microelectromechanical systems (MEMS) applications, currents are confined to the outermost portions of conductors due to the skin effect. Conductors consisting of polymer cores coated with metal, the so-called polymer-core conductor, are appropriate to consider for these applications, and in many instances are easier to fabricate than their solid-metal-core counterparts. Implementation of polymer-core conductors using an SU-8 epoxy-core patterning and subsequent metal electrodeposition is reported. The SU-8 core approach allows for relatively simple formation of extremely high-aspect-ratio columns for inductor sidewalls. In addition, an SU-8 bridge fabrication technique has been realized using a double exposure and single develop scheme. The bridge thickness has been characterized as a function of the optical dose and the post bake time in an oven. Three-dimensional, high-aspect-ratio, high Q-factor, solenoid-type RF inductors are fabricated and tested to demonstrate the feasibility of the polymer-core conductor approach for RF applications. A single, vialess metallization over SU-8 back-bone structure provides the complete conducting paths of the inductor. A single turn inductor that is 900 /spl mu/m in height and 600 /spl mu/m in lateral extension shows a maximum Q-factor of 84 and an inductance of 1.17 nH at 2.6 GHz.     

Arrays of monocrystalline silicon micromirrors fabricated using CMOS compatible transfer bonding

In this paper, we present CMOS compatible fabrication of monocrystalline silicon micromirror arrays using membrane transfer bonding. To fabricate the micromirrors, a thin monocrystalline silicon device layer is transferred from a standard silicon-on-insulator (SOI) wafer to a target wafer (e.g., a CMOS wafer) using low-temperature adhesive wafer bonding. In this way, very flat, uniform and low-stress micromirror membranes made of monocrystalline silicon can be directly fabricated on top of CMOS circuits. The mirror fabrication does not contain any bond alignment between the wafers, thus, the mirror dimensions and alignment accuracies are only limited by the photolithographic steps. Micromirror arrays with 4/spl times/4 pixels and a pitch size of 16 /spl mu/m/spl times/16 /spl mu/m have been fabricated. The monocrystalline silicon micromirrors are 0.34 /spl mu/m thick and have feature sizes as small as 0.6 /spl mu/m. The distance between the addressing electrodes and the mirror membranes is 0.8 /spl mu/m. Torsional micromirror arrays are used as spatial light modulators, and have potential applications in projection display systems, pattern generators for maskless lithography systems, optical spectroscopy, and optical communication systems. In principle, the membrane transfer bonding technique can be applied for integration of CMOS circuits with any type of transducer that consists of membranes and that benefits from the use of high temperature annealed or monocrystalline materials. These types of devices include thermal infrared detectors, RF-MEMS devices, tuneable vertical cavity surface emitting lasers (VCSEL) and other optical transducers.     

一种RF MEM电感及其LC低通滤波器的模拟和设计

模拟并设计了一种基于表面微机械加工的平面MEM电感,提出了它的等效电路模型并给出模型中参数的提取方法。由模拟结果验证了该等效电路具有较高的精度,误差在8%以内。设计的一个3.6nH的平面MEM电感的品质因数超过20,自谐振频率超过15GHz。由平面MEM电感构成的5阶LC低通滤波器的-3dB带宽为3.7GHz,0~3GHz内的插入损耗低于1dB。     

The effect of a metal PGS on the Q‐factor of spiral inductors for RF and mm‐wave applications in a 28‐nm CMOS technology

In this paper, the effect of a metal patterned ground shield (PGS) on the performance of monolithic inductors is investigated. To this aim, three spiral inductors integrated in a 28‐nm fully depleted (FD) silicon‐on‐insulator (SOI) CMOS technology are analyzed by means of a 3‐D FEM‐based commercial software. The inductors have been designed at different operating frequencies in the RF and mm‐wave ranges to better explore the effect of the PGS. Extensive analysis revealed that the shield is able to improve the quality factor (Q‐factor) only of the inductor operated at the lowest frequency (ie, K‐band). On the contrary, it has a detrimental effect on the Q‐factor of the inductors working at higher frequencies. This is mainly due to induced losses in the PGS itself, which are so high to frustrate the substrate loss reduction. This result gives a different perspective to the adoption of the PGS for CMOS integrated inductors, which is largely recommended to improve inductor performance in the current state of the art.     

适用于RF MEMS能量耦合传输的高Q值电感

利用MEMS微电镀工艺技术制作了一种新型的适用于RF MEMS能量耦合传输的高Q值电感,采用ANSOFT公司的HFSS优化平面螺旋电感的结构。在具有高电阻率的玻璃衬底上溅射0.5μm的铜层作为下电极;PECVD淀积厚度为1μmSiO2作为中间介质层;在介质层上结合厚胶光刻技术电镀厚为22μm的铜作为电感线圈。这套电感制作工艺流程简单、易于与IC制备工艺集成。本文制备的微机械电感在微型植入系统中具有广阔的应用前景。测量结果表明:当工作频率在1GHz左右时,微电感的电感值达到55nH,Q值最大可达到25。     

Analysis of modeling approaches for on‐chip spiral inductors

The recent modeling approaches for on‐chip spiral inductors are extensively investigated and compared. The key features of the models are detailedly analyzed. By actual implementation of each model's parameter extraction procedure, the pros and cons of equivalent circuit topologies, parameter extraction techniques, and fitting capacity of models are provided, including 1‐π, 2‐π, and T‐models. 1‐π models and T‐models are proved to be adequate for modeling distributed effect. 2‐π models are more convenient in fitting asymmetric inductors. The transfer function of the spiral inductor is employed in the singularity analysis of the models. The proposals are verified by measured the S‐parameters of 10 fabricated CMOS spiral inductors up to 40 GHz. © 2012 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2012.     

Modeling, optimization and performance of high-Q MEMS solenoid inductors

Modeling, optimization and performance of on-chip solenoid inductors is presented. MATLAB is used to get the π-equivalent circuit model parameters. The effects of the geometrical parameters on the inductance and quality factor (Q-factor) are different. Normally, the performance of the inductors can be improved by increasing the coil turns in a way and increasing the length of the conductor, but both of them will occupy more chip area, which is not good for the minimization of the on-chip system. It is desirable to improve the performance of inductor by increasing the height of the via. Of the three types of fabricated inductors covering the same area, the inductors with the height of via 15, 30 and 45 μm have high performance. The self-resonant frequency is up to 10 GHz. The inductances and Q-factors at peak-Q frequency (about 5.8 GHz) are 1.16, 1.35, 1.78 nH and 21.9, 27, 38, respectively.     

High-Q Solenoid Inductors With a CMOS-Compatible Concave-Suspending MEMS Process

This paper presents micromachined solenoid inductors that are fabricated in a standard CMOS silicon substrate (with a resistivity of 1-8 Omega . cm). The solenoid is concavely embedded in a silicon cavity with the silicon wafer surface remaining a plane, and mechanically suspended to form an air gap from the bottom of the silicon cavity. In addition to facilitating flip-chip packaging, this so-called "concave-suspending" technique effectively depresses the substrate effects including eddy current and capacitive coupling between the coil and the substrate, therefore contributing to both high Q -factor and high resonant frequency of the inductors for high-performance radio-frequency (RF)/microwave integrated circuit applications. Various inductors with different solenoid layouts, e.g., several shapes of curved solenoids, have been successfully fabricated by using a post-CMOS microelectromechanical systems process that employs copper electroplating, tetra-methyl-ammonium hydroxide (TMAH) + iso- propanol etching and compensation control for convex-corner undercutting, photoresist spray coating, XeF₂ gaseous etching, and other steps. A lumped circuit model that accounts for inter- turn fringing capacitance, capacitance between the coil and the substrate, substrate ohmic loss and substrate capacitance, etc., is derived for the solenoid inductors. The accuracy of the model is confirmed by the testing results and can be used for optimal design of the inductors. By S-parameter testing, various types of inductors with different solenoid layouts have been evaluated. The solenoid inductors generally exhibit improved RF performance in Q-factor and self-resonance frequency compared to their conventional counterparts.     

Design and fabrication aspects of an S-shaped film actuator based DC to RF MEMS switch

This paper reports on design and fabrication aspects of a new microelectromechanical series switch for switching dc and RF signals. The switch consists of a flexible S-shaped film with the switching contact, rolling between a top and a bottom electrode in electrostatic touch-mode actuation. This design allows a low actuation voltage independent of the contact distance in the off-state. With a large contact distance, large overlapping switching contact areas are possible by obtaining a high off-state isolation. The RF transmission line and the MEMS part of the switch are fabricated on separate wafers, allowing an implementation of the switch with different RF substrates. The final assembly is done on device level for the first prototypes, even though the design provides the possibility of an assembly by full wafer bonding, leading to a near-hermetic package integrated switch. The measured prototype actuation voltages are 12 V to open and 15.8 V to close the contacts, with a resistance of 275 m/spl Omega/ of each contact at an estimated contact force of 102 /spl mu/N. The measured RF isolation with a contact distance of 14.2 /spl mu/m is better than -45 dB up to 2 GHz and -30 dB at 15 GHz, at a large nominal switching contact area of 3500 /spl mu/m/sup 2/.     

Cubic millimeter power inductor fabricated in batch-type wafer technology

A hybrid technology for the realization of three-dimensional (3-D) miniaturized power inductors is presented. Our devices consist of planar Cu coils on polyimide substrates, and mm-size ferrite magnetic cores, obtained by three-dimensional micro-patterning of ferrite wafers using powder blasting. The coils are realized using an in-house developed high-resolution polyimide spinning and Cu electroplating process. Winding widths down to 5 /spl mu/m have been obtained and total device volumes are ranging between 1.5 and 10 mm/sup 3/. Inductive and resistive properties are characterized as a function of frequency; inductance values in the 100 /spl mu/H range have been obtained.     

“Ni–Zn铁氧体颗粒–光刻胶”覆盖的 片上射频电感

本文报道了采用新型"纳米颗粒一光刻胶"混合旋涂技术制作的片上射频Ni-Zn铁氧体磁膜微电感.成相良好的Ni0.3Zn0.6Cu0.1Fe2O4铁氧体纳米颗粒在光刻胶中均匀混合,再将该混合物涂覆在螺旋电感线圈上,实现电感性能的提升.这种新型低温工艺避免了常规制作铁氧体器件方法带来的高温处理(>600℃)对集成电路的破坏.与无磁膜覆盖样品对比,铁氧体覆盖电感的电感量在0.1～4 GHz提升了14～27%.这是实现高性能、全兼容铁氧体集成片上RF IC电感的一种很有前景的途径.     

High current handling capacity multilayer inductors for RF and microwave circuits

We present test data for several spiral inductors with improved quality factor fabricated on GaAs substrates using the ITT MSAG (multifunction self aligned gate) multilayer process. It is shown experimentally that the quality factor of spiral inductors can be enhanced by using thick metallization and placing inductors on a thick polyimide layer which is placed on top of the GaAs substrate. Using this technique we observed up to 68% improvement in the quality factor of spiral inductors as compared to standard spiral inductors. Inductors having thick metallization can also handle DC currents as large as 0.5 A. © 2000 John Wiley & Sons, Inc. Int J RF and Microwave CAE 10: 139–146, 2000.     

片上射频磁介质电感的设计与仿真

片上无源电感是RF IC中需求很高的器件.将适宜的磁材料引入到射频微电感中,既可有效地提升电感L值,从而使电感所需面积减小,又能保持甚或提升电感Q值,是实现高性能、小尺寸射频微电感的一种非常有前景的方法.我们设计了不同结构的磁介质微电感,通过软件仿真研究了电感结构和材料参数变化对电感性能的影响,为研制小尺寸、高性能片上磁介质电感提供了理论指导.