硅基铝T形梁MEMS可变电容的设计与模拟

提出了一种新颖的运用于射频通信系统VCO中的RFMEMS可变电容。该电容使用平行板和T形梁结构,使用硅衬底,整个结构由铝材料组成,结构简单,与集成电路工艺兼容,从而能够实现片上可变电容。通过静电力驱动上极板向下运动,电容值相应地发生改变,当上极板加电压从2.4V变化到4.3V时,电容值从0.25pF变化到0.33pF,变化率为中心电容的27%。使用Coventor软件对该器件进行了模拟,给出的模拟结果包括容量、调节范围、瞬时响应、Pullin电压和运用该可变电容的VCO的电路模拟。     

射频微机械可变电容的研究与进展

对国内外有关微机械可变电容的研究做了综合阐述,包括改变介质的可变电容、改变重叠面积的可变电容和改变间隔的可变电容.并对其中有代表性的电容结构进行了说明,对其获得的零偏压下的电容量值、Q值以及调节范围进行了比较.     

新颖的双间隔RF MEM可变电容的设计与模拟

设计了一种可用于射频(RF)通信系统中的MEM平行板可变电容,采用新颖的双间隔(two-gap)结构、金属铝极板、折叠“Y”形支撑和厚度不均的可动极板。用CoventorWare软件模拟了电容的C-V特性,当控制电压从0变化到10V时,RF信号电容相应从0.37pF增加到5.64pF,变容比约为15.24∶1;用HFSS软件模拟了电容的S11参数,电容的品质因数Q在1.8GHz下约为77.78。     

平行耦合传输线梳状滤波器的工程设计

平行耦合多线传输线梳状滤波器是一种优良的微波窄带带通滤波器。在性能相同的各种微波滤器中,其体积最小,特别适合在0.4～6千兆赫的频段上使用。本文介绍梳状滤波器的工程设计方法,计标公式和各表。     

基于Ba_xSr_(1-x)TiO_3薄膜电容的L波段可调滤波器

在蓝宝石基片上使用Ba_xSr_(1-x)TiO_3(BST)铁电薄膜电容作为可调元件制作出一种五阶梳状线可调带通滤波器。通过对BST平行板电容的材料特性(介电常数、损耗和可调率)的提取,其中40 V偏压下的可调率为43.1%,将这些特性运用于可调滤波器的制作。初步的实验结果分析表明,在20V直流偏置电压作用下,滤波器的中心频率从1.19GHz变化到1.31GHz(可调率为10.1%),带内插入损耗为13.5~13.7dB,回波损耗低于12dB。     

圆内导体板线带通滤波器的设计

首先从圆内导体板线基本原理出发，推出等直径圆内导体耦合线中的自电容，互电容公式，其次通过选择归一代特性导纳Ｙａｉ／Ｙ及自编Ｃ语言程序的迭代计算，使滤波器自电容，互电容符合矩形内导体结构的梳状线带通滤波器的自，互电容。     

基于DSPSL 的电可重构平面带通滤波器

提出基于新型平衡传输线——双面平行带线(DSPSL)结构的电容加载电可重构平面带通滤波器,并以梳状线 和磁耦合谐振环带通滤波器为例验证该方案的可行性。相对于常见的微带线结构,双面平行带线具有对称性以及较高 的功率使用容量。这些特性使得滤波器在没有无限大金属地板的情况下,仍然获得了良好的性能。采用DSPSL 结构 进行微波电路设计不但可以减小电路的尺寸,同时还增加了电路设计的灵活性。     

发光二极管负电容与角频率的关系

利用正向交流(AC)小信号方法对发光二极管(LED)的电容-电压特性进行测量,可以观察到发光二极管中的负电容现象.提出了测量到的负电容现象是表象,不存在负电容;发光二极管p-n结的结电容在特定的正向电压范围内等效于可变电容.分析可变电容对交流小信号响应得到:特定参数的可变电容使电流的相位移相π,使得在测量中表现为负电容;得到了发光二极管负电容与角频率的关系表达式.     

发光二极管负电容与角频率的关系

利用正向交流(AC)小信号方法对发光二极管(LED)的电容-电压特性进行测量,可以观察到发光二极管中的负电容现象.提出了测量到的负电容现象是表象,不存在负电容;发光二极管p-n结的结电容在特定的正向电压范围内等效于可变电容.分析可变电容对交流小信号响应得到:特定参数的可变电容使电流的相位移相π,使得在测量中表现为负电容;得到了发光二极管负电容与角频率的关系表达式.     

一种采用开关阶跃电容的压控振荡器(上):调谐特性的理论分析

针对采用阶跃可变电容的电感电容压控振荡器电路,本文提出了一种振荡器调谐特性的时域分析方法--周期计算技术. 通过对电感电容谐振回路中电感的I-V曲线分析,详细地阐述了阶跃可变电容能够实现线性压控的物理机理和本质. 对差分调谐电感电容压控振荡器的调谐特性也进行了详细的分析. SPICE电路仿真验证了调谐特性理论分析的正确性.     

一种新偏压结构的BST电容梳状滤波器设计

介绍了一种五阶可调抽头式梳状线滤波器,设计采用共面方式接地,使用Ba0.6Sr0.4TiO3 (BST)铁电薄膜平板电容作为可调部件,并分析了平板电容结构的影响.针对梳状电调滤波器需单阶加压和外接大电阻繁琐的情况,提出利用集成在衬底上的大容量BST电容作为隔离电容,将各阶谐振器的偏压线互连来简化加压过程.运用高频电磁仿真软件HFSS进行验证,设计出的滤波器中心频率可调范围为842～960 MHz(14％),3 dB带宽为9％～10％.     

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.     

Analysis and modeling of liquid-crystal tunable capacitors

Three different configurations of liquid-crystal tunable capacitors were investigated, including fractal structures, comb structures, and square structures. The tuning ranges of the fractal structures, the comb structures, and the square structures at 4 GHz from 0 to 5 V were found to be 8.81%, 7.17%, and 11.85%, respectively. The square structures have the largest tuning ranges mostly because of the uniform electric fields dominated. The Q-values of the fractal structures, the comb structures, and the square structures at 4 GHz with an operation voltage of 5 V were 68.2, 98.3, and 31.0, respectively. Compared to the other two structures, the square structures perform the highest inductive effects, leading to the lowest Q-values. In addition, the liquid crystals with different chiral doping concentrations were injected into the capacitor structures to investigate the impact of different liquid crystals on the tunable capacitors. The threshold voltages (V/sub th/) increase as the chiral doping concentrations enlarge. The steepness of the C-V curves increases as the chiral doping concentrations reduce. Furthermore, a liquid-crystal capacitor model was developed to qualitatively illustrate the performance of the liquid-crystal tunable capacitors. The model prediction and the measurement results were highly correlated.     

静电梳齿驱动器薄膜变形反射镜

提出一种大冲程静电梳齿驱动器微机械薄膜变形反射镜,理论上研究了静电梳齿驱动器微机械薄膜变形反射镜的静电驱动力和变形位移与驱动电压的关系,分析了变形反射镜的驱动稳定性,比较了平板电容驱动器与纵向梳齿驱动器的驱动能力.结果表明,变形反射镜的静电驱动力和变形位移没有关系;在相同的面积下,纵向梳齿驱动器的驱动力比平板电容驱动器的驱动力大很多.     

Two movable-plate nitride-loaded MEMS variable capacitor

A microelectromechanical systems (MEMS) variable capacitor having two movable plates loaded with a nitride layer is proposed. A trench in the silicon substrate underneath the capacitor is used to decrease the parasitic capacitance. The use of an insulation dielectric layer on the bottom plate of the MEMS capacitor increases the capacitor's tuning range and eliminates stiction. Experimental and theoretical results are presented for two capacitors having different capacitance values. The measured tuning range is found to be 280% at 1 GHz. The achievable tuning range far exceeds that of the traditional parallel-plate MEMS variable capacitors. The proposed MEMS variable capacitor is built using the MetalMUMP's process.     

Rotational Driven RF Variable Capacitors With Post-CMOS Processes

A ring-shaped on-chip tunable capacitor is proposed and fabricated with CMOS-compatible micromachining processes for radio frequency integrated circuits (RFICs). The rotationally driven variable capacitor features a much higher axial mechanical stiffness compared to its conventional straight-line-driven counterpart, and therefore, can effectively depress the instability caused by environmental vibration when the varactor is used in mobile systems. Meanwhile, the rotationally driven intedigitated capacitor is designed to be very flexible for wide range of electrostatic tuning. Near-room-temperature micromachining techniques are developed for post-CMOS integrating the tunable capacitors into RFIC chips. The fabricated varactor is measured with a tuning ratio of 2.1:1 under an actuation of 12 V. Q-factor is measured as 51.3 at 1 GHz and 35.2 at 2 GHz, while self-resonance frequency is as high as 9.5 GHz. The rotationally driven tunable capacitor shows about two orders of magnitude higher antivibration capability compared to the conventional straight-driven one. Therefore, the high-performance CMOS-compatible tunable capacitors are promising for practical RFIC applications in mobile electronic telecom systems.     

Accurate high speed empirically based predictive modeling of deeplyembedded gridded parallel plate capacitors fabricated in a multilayerLTCC process

A novel technique is presented for the accurate, rapid, high frequency, predictive modeling of parallel plate capacitors with gridded plates manufactured in a multilayer low temperature cofired ceramic (LTCC) process. The method is empirical in nature and is based on the concept of incrementally constructing the model for a structure from well characterized individual building blocks. Building blocks are characterized by the use of test structures and measurements, and are modeled using passive lumped circuit elements. This method is applied to the predictive modeling of deeply embedded gridded parallel plate capacitor structures. The procedure has been experimentally verified, with accurate predictions of behavior obtained up to the second self resonance for large area gridded parallel plate capacitors. Since lumped element circuits are generated by this method, structure prediction speed is determined by circuit size and simulator small signal analysis time. The method is versatile and is well suited for circuit design applications     

Effect of etch holes on the capacitance and pull-in voltage in MEMS tunable capacitors

Microelectromechanical systems (MEMS) tunable capacitors, switches or actuators are widely applied in wireless communication systems. In the fabrication process etch holes are used to release the sacrificial layer with relatively large structures, which obviously affects the performance of devices. However, most researchers neglect this effect during their designing of the capacitors, switches or actuators. This article presents the theoretical calculation of the capacitance of tunable capacitors with etch holes, and analyses the deviation of the capacitance and pull-in voltage with different parameters such as the length of the plates w, the length of the etch holes w _h, the air gap between the two plates d, and the number of the etch holes. To validate the theory in this article, a tunable capacitor was fabricated by surface micromachined technology. The theoretical results compare well with the experimental results.     

A new actuation mechanism for an Interfacial Force Microscope: Design,implementation, and feedback control

In this paper we present development of a sensing and actuation mechanism along with its controller for an Interfacial Force Microscope. The device can be used as a micro-scale force sensor or actuator using a feedback control scheme that regulates the interaction force between the probe tip and the sample. The mechanism is essentially a force balancing system consisting of a torsion bar and two variable gap parallel plate capacitors with a sharp probe attached to the moving plate of one of the capacitors. The capacitors are utilized to measure the air gap distance and act as electrostatic actuators to compensate the force applied to the sensor tip. Given that the system is nonlinear with respect to the control input, a nonlinear feedback linearization scheme coupled with a dynamic output feedback controller is developed and integrated with available measurement and computing hardware. The dynamic controller requires measurement of position information only and provides improved performance when compared to conventional controllers. Experimental studies are conducted for nanoindentation and imaging applications and performance of the controller is evaluated.     

OTA-based integrable voltage/current-controlled ideal C-multiplier

A capacitance multiplier circuit, using operational transconductance amplifiers, is realised. The circuit provides widerange linear control of the capacitance value with direct voltage or current. This makes the realisation of large-valued grounded capacitors possible in IC fabrication. The linearly tunable capacitor is expected to find attractive applications in voltage/current-controlled filters, oscillators etc.