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.     

Electrostatically driven tunable radio frequency inductor

An electrostatically driven tunable radio frequency (RF) inductor with large inductance tuning range consisting of electroplated soft magnetic permalloy (Ni₈₀Fe₂₀ alloy) plate was proposed in this paper. The fabricated tunable inductor exhibits a large tunable inductance range up to 77.8%, together with improved quality factor (Q-factor) at high frequencies. Such tunability of inductance and Q-factor was due to the magnetoelectric coupling effect between the soft magnetic permalloy plate and the spiral inductor, which lead to the magnetic flux of the inductor and mutual inductance change. The concept of tuning inductance by using electroplated soft magnetic permalloy has large potential for wide range RFIC applications.     

High aspect ratio air core solenoid inductors using an improved UV-LIGA process with contrast enhancement material

In this paper, we investigate the application of a contrast enhancement material (CEM388SS^®, Shin-Etsu MicroSi, Inc., AZ, USA) on thick SU-8 negative photoresist (Microchem Corp., MA, USA) and its use in the construction of a high aspect ratio on-chip solenoid inductor. Various SU8 test microstructures (with aspect ratio of 10:1 and 20:1) were first constructed by utilizing this improved UV-LIGA process to demonstrate the clear difference before and after the application of CEM. It was found that this material dramatically reduced the “T-topping” effect and improved the structural profile angle; and higher aspect ratio microstructures could be achieved without modification/upgrades of any kind on the existing lithography tool. Furthermore, we implemented this process in the fabrication work of high aspect ratio air core solenoid inductor and obtained a very high quality (Q) factor of 72.8 at 9.7 GHz from a 3-turn inductors and a high inductance of 28 nH from a 20-turn inductor. Experimental data showed that inductors with taller via structures (higher aspect ratio) had better radio frequency (RF) characteristics than those of lower via structures, which are highly desirable in many communication applications.     

A wireless powered fully integrated SU-8-based implantable LC transponder

In this work, we report a SU-8-based fully integrated miniaturized inductively powered LC transponder for generic implantable wireless sensor applications. It consists of a 1 mm diameter octagonal spiral inductor and a micro fabricated MIM (metal insulator metal) capacitor. Polyvinylidene Fluoride–Trifluoroethylene (PVDF–TrFE) copolymer is applied as a dielectric material for the capacitor fabrication due to its high dielectric constant. The 1 mm diameter, 154 nH spiral inductor is built on top of the capacitor. The capacitor and the inductor are in parallel connection through SU-8 via holes. SU-8 is used as a packaging material due to its biocompatibility, and also it serves as an insulator between the capacitor and the spiral inductor. The operating frequencies of the LC tanks are decided by the sizes of the capacitors (45 × 45, 55 × 55, 95 × 95 and 100 × 100 μm), and measured operating frequency range is from 385 to 485 MHz. The fabricated LC tanks are held to the power transmitting coil coaxially at distances of 2, 5, 7 and 10 mm, and rectified induced voltage at the LC tank is 8.5 V with 29 dBm input power at a 5 mm distance.     

恒流源充电二极管放电的电感式位移传感器

介绍恒流源充电二极管放电的电感式位移传感器,其电感值的测量原理是采用开关电路,以恒流源电路向电感线圈充电,只经过二极管放电,定时测量稳定放电的时间来测量电感值。其位移量是通过测量线圈的电感值来间接测量的。分别论述了单向和双向充放电测量电感值的原理,并设计了电感式和电涡流式两种测量位移量的试验,通过试验和数据分析证明这种电感式测量位移的方法可行,不采用高频正弦激励,即可测量较小的电感值(μH)。     

“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.     

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.     

Modeling double‐side printed meander‐line inductors on printed circuit boards

A lumped element model for a double‐side printed meander‐line inductor with closed‐ form expressions for the electrical model parameters L, C, R_l, and R_c is presented. These structures are cheaper than coils and need less area per unit of inductance than single‐side printed meander‐line inductors. The model has been validated with measurements from 30 to 1000 MHz, finding a mean error in the inductance parameter of about 1%. © 2003 Wiley Periodicals, Inc. Int J RF and Microwave CAE 13: 105–112, 2003.     

LDC1000电感数字传感器的转速测量设计

不同于传统检测转速的方法,本测量方法在金属齿轮转速的检测方法中提出了新的设计思路,以LDC1000电感数字传感器为核心,以低功耗、低成本的MSP430F149为主控芯片,加上自制电感线圈来完成转速测量.射频收发芯片nRF24L01作为转速信息数据传输装置,发展前景良好.本文分析了转速测量的理论依据,给出电路原理图及其程序流程,实现对金属齿轮的转速测量、数据的传输共享.     

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.     

Enhancement of metal coil quality on selective p-silicon based planar electromagnetic coil by thermal annealing process

In this paper we report an optimization of metal quality of planar MEMS electromagnetic coil through thermal annealing process. The study aims to see the effects of annealing process on the quality of metal layer deposited on localized p-type silicon regions. Two annealing process parameters namely isothermal (annealing under time variations in constant temperature) and isochronal (annealing under temperature variations at constant time) were performed on metal contact on highly doped Si substrate and characterized using transfer length method method by measuring the specific contact resistance ρ _C of the metal traces. The measurement results showed that the annealing process have significant influence on physical and electrical characteristics of the metal layer. Analysis showed that the quality of metal layer was significantly improved through the annealing process after treatment at temperature variations between 425–550 °C. An optimum annealing at 525 °C for 15 min was observed and the contact resistance can be reduced significantly up to 400 %. The results also showed that the surface roughness improves while metal contact resistance decreases 40 times when the metal is annealed for more than 10 min. The planar coil structure was designed to reduce the device density of a compact magnetic micro-sensor system.     

Characterization of flexible RF microcoils dedicated to local MRI

In magnetic resonance imaging (MRI), the electrical performance of the RF coil is critical to achieve sufficient signal to noise ratio (SNR), especially when microscopic structures [about (100 μm)³] have to be observed. In this field of application, we have developed a device (microcoil) based on the original concept of monolithic resonator, dedicated to superficial region imaging (human skin) or small animal imaging. This paper presents the developed process based on micromoulding. Flexible thin films of polymer have been used as dielectric substrate so that the microcoil could be form-fitted to non-plane surfaces. First, electrical characterizations of the RF coils have been performed. The results were compared to the expected values. A flexible RF coil of 15 mm diameter was then used to perform proton MRI of a saline phantom. When the coil was form-fitted to the phantom surface, a maximum SNR gain of 2 was achieved with respect to identical but plane RF coil. Finally, the flexible coil was used to perform MRI in vivo with high spatial resolution on a mouse using a small animal dedicated scanner operating at 2.35 T.     

Design,optimization and simulation of a low-voltage shunt capacitive RF-MEMS switch

This paper presents the design, optimization and simulation of a radio frequency (RF) micro-electromechanical system (MEMS) switch. The capacitive RF-MEMS switch is electrostatically actuated. The structure contains a coplanar waveguide, a big suspended membrane, four folded beams to support the membrane and four straight beams to provide the bias voltage. The switch is designed in standard 0.35 µm complementary metal oxide semiconductor process and has a very low pull-in voltage of 3.04 V. Taguchi method and weighted principal component analysis is employed to optimize the geometric parameters of the beams, in order to obtain a low spring constant, low pull-in voltage, and a robust design. The optimized parameters were obtained as w = 2.5 µm, L1 = 30 µm, L2 = 30 µm and L3 = 65 µm. The mechanical and electrical behaviours of the RF-MEMS switch were simulated by the finite element modeling in software of COMSOL Multiphysics 4.3^® and IntelliSuite v8.7^®. RF performance of the switch was obtained by simulation results, which are insertion loss of ?5.65 dB and isolation of ?24.38 dB at 40 GHz.     

Fabrication and properties of integrated magnetic inductors using an RLC model which takes into account eddy current

This article concerns the development, the fabrication and the characterization of integrated inductors using magnetic layers for use in power electronics. Properties of inductors were extracted using an electrical model which takes into account eddy current. Inductors with one and two magnetic layers were fabricated with thicknesses varying between 100 and 500 µm. Measurements carried out with a Vector Network Analyzer up to 350 MHz are presented. The results show that the use of one magnetic layer allows the inductance of the coreless inductor to be multiplied by two and an inductor with two magnetic layers allows the inductance of the coreless inductor to be multiplied by 15 for 500 µm magnetic thickness layers.

     

Design and modeling of a continuously variable piezoelectric RF MEMS switch

A structure for a piezoelectrically actuated capacitive RF MEMS switch that is continuously variable between the ON state and the OFF state has been proposed. The device is based on variable capacitance using a cantilever fixed at both ends that is actuated using a lead zirconate titanate thin film. Because the device is contactless, the reliability issues common in contact-type RF MEMS switches can be avoided. A comprehensive mathematical model has been developed in order to study the performance of the device, and allow for design optimization. Electrical measurements on test structures have been compared with the performance predicted by the model, and the results used to design a prototype RF MEMS switch. The model and simulations indicate the proposed switch structure can provide an insertion loss better than 0.7 dB and an isolation of more than 10 dB between 6 and 14 GHz with an actuation voltage of 22.4 V. The state of the device is continuously variable between the ON state and the OFF state, with a tunable range of capacitance of more than 15\(\times \).     

Large tuning ratio high aspect ratio variable capacitors using leveraged bending

Variable capacitors are a key component in Radio Frequency Micro Electro-Mechanical Systems (RF MEMS). They comprise fixed and flexible electrodes. Deformation, or actuation, of the flexible electrode changes the capacitance of the capacitor. This way, electrical properties of high frequency circuits can be modified. Traditionally, variable capacitors are based on a planar layout architecture, while a newer, vertical-wall, quasi three-dimensional approach theoretically enables increased device performance. Such devices depend on high aspect ratios, i.e. relatively high micro structures with very thin walls and gaps. A few vertical-wall variable capacitors made of nickel or gold have been fabricated to date, using deep X-ray lithography and subsequent electroplating (Achenbach et al. 2006; Klymyshyn et al. 2007, 2010) as the fabrication approach. They feature, amongst others, excellent quality factors of Q ≤ 95 at 5.6 GHz with 50 Ω reactance, but suffer from a very limited tuning range of the capacitance value (tuning ratio of, e.g., 1.38:1). The devices presented here exploit the same architecture and materials selection, resulting in similar, excellent Q-factors, but feature a different electrode layout approach, referred to as leveraged-bending. This layout is based on pulling a flexible electrode sideways, towards a fixed electrode, increasing the capacitance when actuating the variable capacitor. The leveraged bending approach theoretically enables infinitely high tuning ratios for components with perfect structure accuracy. To date, a significantly increased tuning ratio of 1.9:1 has been demonstrated. Limiting factors are an electrically non-ideal layout geometry chosen as a compromise to increase the fabrication yield, and structure deviations of ~1.6 μm from CAD layout to the electroplated component. Electrostatic actuation requires voltages between 0 and 72 V for capacitance values on the order of C = 0.3 pF at device dimensions of about 1.5 mm overall length, 5–10 μm gap and wall widths, and 100 μm metal height. Device performance measured with a vector network analyzer is in 97 % agreement with simulation results based on two-dimensional electrostatic-structural coupling (ANSYS Multiphysics) and three-dimensional electromagnetic field simulations (Ansoft HFSS). These simulations also indicate that an optimized gap geometry will allow to reduce the actuation voltage required by up to 40 %.     

Novel efficient method for inductance calculation of inductors with optimized layout

In this article, we consider the computing of conformal modules and their application for inductance calculation of spiral inductors with optimized layout. We present a novel and efficient method for inductance and quality factor calculation of inductors with a variable conductor width. The computed inductance is compared with earlier published experimental data and very good agreement is achieved. © 2006 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2006.     

High quality factor copper inductors integrated in deep dry-etched quartz substrates

This paper reports on an inductor fabrication method capable to deliver high quality factor (Q) and high self-resonance frequency (SRF) devices using quartz insulating substrates and thick high-conductivity copper lines. Inductors are key devices in RF circuits that, when fabricated on traditional semiconductor substrates, suffer from poor RF performances due to thin metallization and substrate related losses. Many previous works revealed that RF performances are strongly dependent on the limited metallization thickness and on the conductivity of the substrate. In this paper we demonstrate a new fabrication process to improve the Q factor of spiral inductors by patterning thick high conductive metal layers directly in a dielectric substrate. Moreover, we develop and validate accurate equivalent circuit modeling and parameter extraction for the characterization of the fabricated devices.     

Wetting considerations in capillary rise and imbibition in closed square tubes and open rectangular cross-section channels

The spontaneous capillary-driven filling of microchannels is important for a wide range of applications. These channels are often rectangular in cross-section, can be closed or open, and horizontal or vertically orientated. In this work, we develop the theory for capillary imbibition and rise in channels of rectangular cross-section, taking into account rigidified and non-rigidified boundary conditions for the liquid–air interfaces and the effects of surface topography assuming Wenzel or Cassie-Baxter states. We provide simple interpolation formulae for the viscous friction associated with flow through rectangular cross-section channels as a function of aspect ratio. We derive a dimensionless cross-over time, T _c, below which the exact numerical solution can be approximated by the Bousanquet solution and above which by the visco-gravitational solution. For capillary rise heights significantly below the equilibrium height, this cross-over time is T _c ≈ (3X _e/2)^2/3 and has an associated dimensionless cross-over rise height X _c ≈ (3X _e/2)^1/3, where X _e = 1/G is the dimensionless equilibrium rise height and G is a dimensionless form of the acceleration due to gravity. We also show from wetting considerations that for rectangular channels, fingers of a wetting liquid can be expected to imbibe in advance of the main meniscus along the corners of the channel walls. We test the theory via capillary rise experiments using polydimethylsiloxane oils of viscosity 96.0, 48.0, 19.2 and 4.8 mPa s within a range of closed square tubes and open rectangular cross-section channels with SU-8 walls. We show that the capillary rise heights can be fitted using the exact numerical solution and that these are similar to fits using the analytical visco-gravitational solution. The viscous friction contribution was found to be slightly higher than predicted by theory assuming a non-rigidified liquid–air boundary, but far below that for a rigidified boundary, which was recently reported for imbibition into horizontally mounted open microchannels. In these experiments we also observed fingers of liquid spreading along the internal edges of the channels in advance of the main body of liquid consistent with wetting expectations. We briefly discuss the implications of these observations for the design of microfluidic systems.