Flip chip assembled MEMS inductors

High performance suspended MEMS inductors produced using a flip chip assembly approach are described. An inductor structure is fabricated on a carrier and then flip chip assembled onto a substrate to form a suspended inductor for RF-IC applications with significant improvement in Q-factor and frequency of operation over the conventional IC inductors. A spiral MEMS inductor has been successfully produced on a silicon substrate with an air gap of 26 /spl mu/m between the inductor structure and the substrate. The inductance of the device was measured to be /spl sim/2 nH and a maximum Q-factor of 19 at /spl sim/2.5 GHz was obtained after pad/connector de-embedding.     

Design and modeling of a micromachined high-Q tunable capacitor with large tuning range and a vertical planar spiral inductor

In wireless communication systems, passive elements including tunable capacitors and inductors often need high quality factor (Q-factor). In this paper, we present the design and modeling of a novel high Q-factor tunable capacitor with large tuning range and a high Q-factor vertical planar spiral inductor implemented in microelectromechanical system (MEMS) technology. Different from conventional two-parallel-plate tunable capacitors, the novel tunable capacitor consists of one suspended top plate and two fixed bottom plates. One of the two fixed plates and the top plate form a variable capacitor, while the other fixed plate and the top plate are used to provide electrostatic actuation for capacitance tuning. For the fabricated prototype tunable capacitors, a maximum controllable tuning range of 69.8% has been achieved, exceeding the theoretical tuning range limit (50%) of conventional two-parallel-plate tunable capacitors. This tunable capacitor also exhibits a very low return loss of less than 0.6 dB in the frequency range from 45 MHz to 10 GHz. The high Q-factor planar coil inductor is first fabricated on a silicon substrate and then assembled to the vertical position by using a novel three-dimensional microstructure assembly technique called plastic deformation magnetic assembly (PDMA). Inductors of different dimensions are fabricated and tested. The S-parameters of the inductors before and after PDMA are measured and compared, demonstrating superior performance due to reduced substrate loss and parasitics. The new vertical planar spiral inductor also has the advantage of occupying much smaller silicon areas than the conventional planar spiral inductors.     

Thermal effects in suspended RF spiral inductors

Self-heating effects on integrated suspended and bulk spiral inductors are explored. A dc current is fed through the inductors during measurement to emulate dc and radio frequency power loss on the inductor. A considerable drop in Q by /spl sim/18% at 36.5 mW is observed for suspended coils with 3-/spl mu/m aluminum metallization compared to reference inductors on bulk-Si. Simulations in Ansoft's ePhysics indicate that, due to the thermal isolation of the suspended coil, the power loss from resistive self-heating in the metal has to be transferred outwards through the metal turns. This also results in a thermal time constant. This time constant is measured to be /spl sim/10 ms, meaning that it can affect power circuits operating in pulsed mode.     

双层螺旋RF MEMS电感的模拟与设计

分析了双层螺旋电感的等效电路模型,研究了一种与传统CMOS工艺兼容的MEMS工艺,通过腐蚀电感结构下的硅衬底使电感悬空.利用HFSS软件对一些双层螺旋微电感进行了模拟,模拟结果表明,相比传统单层电感,双层电感可以减少60%的芯片面积,10nH的电感也只需要很小的面积,经过MEMS后处理的双层螺旋电感的最大Q值都超过了20.     

双层悬空结构射频微电感制作研究

利用MEMS工艺制作了一种双层悬空结构的圆形射频微电感,研究了双层结构微电感中微带线宽度对其性能的影响。研究表明,双层悬空结构的圆形射频微电感不仅具有较大的电感量,而且其Q值也较高;双层微电感的Q值随微带线宽度的增大而升高,而电感量则随微带线宽度的增大而降低。对于微带线宽度为60μm的双层微电感,在频率2～4GHz时,其电感量可达到5nH左右,Q值达到20。     

Improvement of the quality factor of RF integrated inductors bylayout optimization

A systematic method to improve the quality (Q) factor of RF integrated inductors is presented in this paper. The proposed method is based on the layout optimization to minimize the series resistance of the inductor coil, taking into account both ohmic losses, due to conduction currents, and magnetically induced losses, due to eddy currents. The technique is particularly useful when applied to inductors in which the fabrication process includes integration substrate removal. However, it is also applicable to inductors on low-loss substrates. The method optimizes the width of the metal strip for each turn of the inductor coil, leading to a variable strip-width layout. The optimization procedure has been successfully applied to the design of square spiral inductors in a silicon-based multichip-module technology, complemented with silicon micromachining postprocessing. The obtained experimental results corroborate the validity of the proposed method. A Q factor of about 17 have been obtained for a 35-nH inductor at 1.5 GHz, with Q values higher than 40 predicted for a 20-nH inductor working at 3.5 GHz. The latter is up to a 60% better than the best results for a single strip-width inductor working at the same frequency     

Balancing temperature dependence of on-wafer SOS inductors

The inductance and the quality factor (Q) of on-wafer inductors have a strong temperature dependence. For balancing unwanted temperature-induced variation, two different layout structures for silicon-on-sapphire (SOS) inductors were studied. One test series used metal inductors with a varying number of vias and the other metal inductors with silicon-based coils added. The tested silicon coil materials were polysilicon and n-diffusion and p-diffusion silicon. At the temperature of 423 K, the metal inductor with the highest number of vias gave less decreased Q. A silicon coil increases the parasitic capacitance of the inductor, which decreases the self-resonant frequency. Thus, the Q of the inductor with the polysilicon coil was equal to or better than that of the plain metal inductor up to the frequency of 8 GHz. Furthermore, the polysilicon coil balanced the temperature dependent variations reflected to the inductance and the self-resonant frequency. The inductor with the polysilicon coil had the best and the most stable characteristics in the measured temperature range, from 233 K to 423 K. The present results are important for the design of System-in-Package (SiP) stacked systems in which local power densities may be increased.     

梳齿式MEMS加速度计在冲击下的失效分析

对Si基梳齿式MEMS加速度计在冲击下进行了失效分析,验证了其主要失效模式,分析了其失效机理。通过机械冲击实验并采用扫描电镜(SEM)、X射线透视系统、扫描声学显微镜(SAM)观察及电性能测试等分析技术,研究了梳齿式MEMS加速度计在冲击载荷下的结构与封装失效,运用材料力学理论加以分析论证,发现悬臂梁断裂是较为主要的失效模式,且此类器件的封装失效主要表现为气密性失效和装配工艺失效,为MEMS器件的可靠性设计提供了重要依据。     

Tunable MEMS Spiral Inductors With Optimized RF Performance and Integrated Large-Displacement Electrothermal Actuators

We propose a tunable microelectromechanical systems integrated inductor with a large-displacement electrothermal actuator. Based on a transformer configuration, the inductance of a spiral inductor is tuned by controlling the relative position of a magnetically coupled short-circuited loop. The magnetic coupling between the inductors can be changed from 0.17 to 0.8 through an electrothermal actuator that can change their relative position by over 140 mum . For the first time, we investigate the impact of this tuning scheme on the inductance and quality factor and propose optimal designs. While a previous preliminary study has focused on keeping the ratio between the two coupled inductors close to one, we find that optimal performance is a weak function of this ratio. Instead, it primarily depends on the resistive loss of the short-circuited coil. Our theoretical studies are backed by a variety of fabricated and measured tunable inductors that show a ~2:1 inductance tuning ratio over a wide frequency range of approximately 25 GHz. In addition, the maximum and minimum quality factors of the tunable inductor are measured to be 26 and 10, respectively, which agree well with the theoretically expected values.     

三维微机械电感的优化设计

研究了影响三维微机械电感电感值和Q值的主要因素 ,提出了电感值和Q值的理论计算模型。并利用该模型 ,对不同尺寸结构的三维微机械电感进行了数值模拟。根据理论计算的结果 ,得到了电感的优化结构 ,在 2 .5GHz的工作频率下 ,其电感值为 11nH ,Q值为 9。     

Micromachined high-Q inductors in a 0.18-μm copper interconnectlow-k dielectric CMOS process

On-chip spiral micromachined inductors fabricated in a 0.18-μm digital CMOS process with 6-level copper interconnect and low-K dielectric are described. A post-CMOS maskless micromachining process compatible with the CMOS materials and design rules has been developed to create inductors suspended above the substrate with the inter-turn dielectric removed. Such inductors have higher quality factors as substrate losses are eliminated by silicon removal and increased self-resonant frequency due to reduction of inter-turn and substrate parasitic capacitances. Quality factors up to 12 were obtained for a 3.2-nH micromachined inductor at 7.5 GHz. Improvements of up to 180% in maximum quality factor, along with 40%-70% increase in self-resonant frequency were seen over conventional inductors. The effects of micromachining on inductor performance was modeled using a physics-based model with predictive capability. The model was verified by measurements at various stages of the post-CMOS processing. Micromachined inductor quality factor is limited by series resistance up to a predicted metal thickness of between 6-10 μm     

一种硅衬底镂空结构的圆形射频微电感

利用MEMS工艺以及硅的湿法刻蚀工艺制作了一种硅衬底镂空结构的圆形射频微电感，并研究了硅衬底背面减薄对射频微电感性能的影响，结果表明：微电感硅衬底经过局部刻蚀减薄后其自谐振频率上升，电感量的频率稳定性提高，而其最大Q值下降。     

Fully Integrated Low Phase-Noise VCOs: From Special Processing to Standard CMOS

An overview is given on the several options for and problems associated with creating high-quality integrated inductors for VCOs. Special processing techniques are reported that can enhance the performance of a normal planar inductor coil. Bonding Wire inductors are presented as an alternative, that allows state-of-the-art phase noise performance at no extra cost. Finally, it is shown that by thorough analysis of standard planar inductors with finite-element simulations, performances can be achieved that are even better than structures requiring extra processing cost. This is done despite a low-ohmic substrate with only two metal layers.     

基于微机电技术的硅基射频电感的设计与仿真

本文对基于微机电技术（MEMS）的硅基射频电感的设计技术进行了介绍,利用三维电磁仿真软件设计了两种不同结构的MEMS电感,给出了相应的等效电路模型并进行了参数提取。     

Flip-Chip-Assembled Air-Suspended Inductors

This paper discusses high-performance planar suspended inductors for hybrid integration with microwave circuits. The inductors are fabricated using a silicon surface micromachining foundry process and assembled using flip-chip bonding. The silicon substrate is removed, leaving a metal inductor suspended 60 mum above the microwave substrate, thus reducing the parasitic capacitance and loss. Various rectangular, octagonal, and circular inductor geometries with one to five windings are designed with inductance values between 0.65 and 16 nH to demonstrate the flexibility of this technique. Measured self-resonant frequencies are between 5 and 34.8 GHz, with quality factors from 45 to 100. Equivalent circuits extracted from measurement for each inductor type show good agreement with measured impedance and full-wave simulations over frequency. The dc current handling limit is 200 mA     

Fabrication and performance of a novel suspended RF spiral inductor

A novel suspended radio frequency (RF) spiral inductor was fabricated on glass substrate by using the microelectromechanical systems (MEMS) technology. The suspended spiral inductor is sustained with the T-shaped pillars. Great improvements in Q-factor have been achieved because of the separation between the substrate and the inductor. In the fabrication process, fine polishing of the photoresist is used to simplify the processes and ensure the seed layer and the pillars contact perfectly, and dry etching technique is used to remove the seed layer. The inductance and Q-factor are measured using the HP 8722D network analyzer in the frequency range of 0.05-10 GHz. The maximum quality factor of this inductor is 37 for the inductance of 4.2 nH with a suspended height of 60 /spl mu/m. Also, the relationship between the maximum quality factor and the suspended height were studied; the maximum quality factor grows gradually with the increase of the suspended height.     

Design and simulation of High Q MEMS LC-tank for oscillators

This research focuses on the design of a high-performance MEMS LC-tank using a high Q MEMS inductor and capacitor. A two different gap varactor has been used to avoid pull-in voltage at 2.4 GHz. The layout has been done by CoventorWare software. The DC voltage is 2.5 v, which is applied to the plates and results of 2.04 pF could be gained. The Q factor of the varactor is computed at about 557.27, which is good enough to make a low-phase noise VCO. A hollow spiral inductor with a silicon base substrate for compatibility with CMOS technology has been designed. The Greenhouse equation has been used to obtain the dimensions of the inductor. A suspended inductor has been implemented to avoid substrate coupling. The simulation has been done by CoventorWare. The Q factor of the inductor has been calculated using Yue's model. The resultant values of inductance and the Q factor at 2.4 GHz, are 2.89 nH and 27, respectively, which are in good agreement with the results of theoretical computation. The results were verified with the well-documented literature.     

MEMS技术制作的螺线管微电感

考虑和分析了螺线管微电感的几何结构参数对微电感性能的影响,利用MEMS技术制作了四种不同几何结构的高性能射频螺线管微电感。这些微电感采用铜线圈,以减小线圈寄生电阻,且制作工艺简单,成本低,与IC相兼容。测试结果表明,微电感在较宽的工作频率范围内具有较高的Q值,在频率分别为6 GHz,4.4 GHz,5.8 GHz和5.6 GHz,微电感Q峰值为38,19.1,24.1和21.9,所对应的电感量为1.81 nH,1.07 nH,1.03 nH和1.17 nH。     

Packaging-compatible high Q microinductors and microfilters forwireless applications

To meet requirements in mobile communication and microwave integrated circuits, miniaturization of the inductive components that many of these systems require is of key importance. At present, active circuitry is used which simulates inductor performance and which has high Q-factor and inductance; however, such circuitry has higher power consumption and higher potential for noise injection than passive inductive components. An alternate approach is to fabricate integrated inductors, in which lithographic techniques are used to pattern an inductor directly on a substrate or a chip. However, integrated inductors can suffer from low Q-factor and high parasitic effects due to substrate proximity. To expand the range of applicability of integrated microinductors at high frequency, their electrical characteristics, especially quality factor, should be improved. In this work, integrated spiral microinductors suspended (approximately 60 μm) above the substrate using surface micromachining techniques to reduce the undesirable effect of substrate proximity on the inductor performance are investigated. The fabricated inductors have inductances ranging from 15-40 nH and Q-factors ranging from 40-50 at frequencies of 0.9-2.5 GHz. Microfilters based on these inductors are also investigated by combining these inductors with integrated polymer filled composite capacitors     

Suspended Spiral Inductor and Band-Pass Filter on Thick Anodized Aluminum Oxide

We make suspended inductors and 2.45 GHz BPFs on the selectively anodized aluminum. The thick anodized alumina is used as the supporting dielectric and it is easily removed by using chemical wet-etching. The thickness of anodized alumina is 80 mum and the depth of the total air-cavity is 200 mum. The fabricated inductor over an air cavity has a 25% greater Q factor and 21% higher inductance at 2 GHz compared to an inductor on anodized aluminum. The 2.45 GHz BPF adjusting the suspended inductors has 2.8 dB of insertion loss with a narrow bandwidth.