RF MEMS开关的设计分析

针对具有低损耗、高隔离度性能的微机电系统(Micro-Electro-Mechanical System,MEMS)开关,介绍了串联DC式和并联电容式的开关结构模型,并对并联电容式MEMS开关的工作原理、等效电路模型和制造工艺流程进行了描述,利用其模型研究了开关的微波传输性能,设计了一款电容耦合式开关并进行了仿真。由仿真结果可得,开关"开态"时的插入损耗在40 GHz以内优于-0.3 dB;开关"关态"时的隔离度在20～40 GHz相对较宽的频带内优于-20 dB。     

高隔离度X波段RF MEMS电容式并联开关

研究了一种新型的、应用于X波段的高隔离度RF MEMS电容式并联开关结构。相比于普通的并联结构,该开关通过共面波导(CPW)传输线与地平面之间的衬底刻槽结构将隔离度提高了7dB,关态时在13.5GHz谐振频率处的隔离度为-54.6dB,执行电压为26V。弹簧梁结构开关的执行电压下降为14V,在11GHz处其隔离度为-42.8dB。通过两个并联开关级联与开关间的高阻传输线构成的π型调谐开关电路,在11.5GHz处的隔离度为-81.6dB。     

高隔离度宽频带MEMS双膜桥开关

利用一种新型双边加直流驱动电极的电容耦合式MEMS并联膜开关与直接接触式并联膜开关进行级联,形成MEMS双膜开关.通过对其尺寸和结构的优化,降低开关阈值电压,Coventor软件模拟表明,开关的阈值电压小于20V;通过对其匹配设计改善开关的高频性能,HFSS软件模拟的结果表明,在DC～20GHz整个频带内,开关的插入损耗优于-0.1dB,反射损耗低于-30dB,隔离度低于-20dB,在 谐振点处隔离度能达到-40dB.     

A DC-contact MEMS shunt switch

This paper presents the design, fabrication, and performance of a metal-to-metal contact micro-electro-mechanical (MEMS) shunt switch. The switch is composed of a fixed-fixed metal beam with two pull-down electrodes and a central DC-contact area. The switch is placed in an in-line configuration in a coplanar waveguide transmission line. This topology results in a compact DC-contact shunt switch and high isolation at 0.1-18 GHz. The isolation at MM-wave frequencies is limited by the inductance to ground and is -20 dB at 18 GHz. The application areas are in wireless communications and high-isolation switching networks for satellite systems     

Fabrication, assembly, and testing of RF MEMS capacitive switches using flexible printed circuit technology

A novel approach for cost effective fabrication, assembly, and packaging of radio-frequency microelectromechanical systems (RF MEMS) capacitive switches using flexible circuit processing techniques is reported. The key feature of this approach is the use of most commonly used flexible circuit film, Kapton-E polyimide film, as the movable switch membrane. The physical dimensions of these switches are in the mesoscale range. For example, electrode area and gap height of a capacitive shunt switch on coplanar waveguide are 2 /spl times/ 1 mm/sup 2/ and 43 /spl mu/m, respectively. Pull-down voltage is in the range of 90-100 V. In the ON state (up-position), the insertion loss is less than 0.3-0.4 dB up to 30 GHz. In OFF state (down-position), the isolation value is about 15 dB at 12 GHz and increases to 36 dB at 30 GHz. These switches are uniquely suitable for batch integration with printed circuits and antennas on laminate substrates.     

All-metal high-isolation series and series/shunt MEMS switches

This paper presents a novel all-metal series switch with several different pull-down electrode geometries. The switch results in an up-state capacitance of 5-9 fF and an isolation of -25 to -30 d8 at 10 GHz. The fabrication process is completely compatible with the standard capacitive (or dc-contact) shunt switch, A dc-30 GHz series/shunt switch is also presented with an isolation of -60 dB at 5 GHz and -42 dB at 10 GHz. This is the highest isolation switch available to-date. The performance is limited by radiation in the CPW lines and not by the series/shunt switch characteristics. The application areas are in high-isolation switches for basestations and satellite systems     

High-isolation CPW MEMS shunt switches. 1. Modeling

This paper, the first of two parts, presents an electromagnetic model for membrane microelectromechanical systems (MEMS) shunt switches for microwave/millimeter-wave applications. The up-state capacitance can be accurately modeled using three-dimensional static solvers, and full-wave solvers are used to predict the current distribution and inductance of the switch. The loss in the up-state position is equivalent to the coplanar waveguide line loss and is 0.01-0.02 dB at 10-30 GHz for a 2-μm-thick Au MEMS shunt switch. It is seen that the capacitance, inductance, and series resistance can be accurately extracted from DC-40 GHz S-parameter measurements. It is also shown that dramatic increase in the down-state isolation (20⁺ dB) can be achieved with the choice of the correct LC series resonant frequency of the switch. In part 2 of this paper, the equivalent capacitor-inductor-resistor model is used in the design of tuned high isolation switches at 10 and 30 GHz     

Phase-noise analysis of MEMS-based circuits and phase shifters

The effect of Brownian, acceleration, acoustic, and power-supply noise on MEMS based circuits has been calculated for MEMS.-based circuits (phase shifters, delay circuits). The calculations are done for capacitive shunt MEMS switches and metal-to-metal contact series MEMS switches. It is found that these effects result in both an amplitude and phase noise, with the phase noise being around 100× larger than the amplitude noise. The phase noise due to Brownian motion is negligible for MEMS switches with k ≃ 1.0 N/m, g₀ > 2 μm, Q > 0.5, and f₀ ≃ 50 kHz. The effect of acceleration and acoustic noise is negligible for a total acceleration noise of 10 g or less and a total acoustic noise of 74-dB sound pressure level. The power-supply noise depends on the bias conditions of the MEMS element, but is negligible for MEMS switches with a bias voltage of 0 V and a total noise voltage of 0.1 V or less. It is also found that metal-to-metal contact series switches result in much less phase noise than standard capacitive shunt switches. The phase noise increases rapidly for low spring-constant bridges (k = 0.24 N/m), low-height bridges, and bridges with a large mechanical damping (Q < 0.3). Also, varactor-based designs result in 30-40 dB more phase noise than switch-based circuits. This paper proves that microwave passive circuits built using MEMS switches (with a proper mechanical design) can be used in most commercial and military applications without any phase-noise penalty     

A fully integrated SOI RF MEMS technology for system-on-a-chip applications

In this paper, a silicon-on-insulator (SOI) radio-frequency (RF) microelectromechanical systems (MEMS) technology compatible with CMOS and high-voltage devices for system-on-a-chip applications is experimentally demonstrated for the first time. This technology allows the integration of RF MEMS switches with driver and processing circuits for single-chip communication applications. The SOI high-voltage device (0.7-/spl mu/m channel length, 2-/spl mu/m drift length, and over 35-V breakdown voltage), CMOS devices (0.7-/spl mu/m channel length and 1.3/-1.2 V threshold voltage), and RF MEMS capacitive switch (insertion loss 0.14 dB at 5 GHz and isolation 9.5 dB at 5 GHz) are designed and fabricated to show the feasibility of building fully integrated RF systems. The performance of the fabricated RF MEMS capacitive switches on low-resistivity and high-resistivity SOI substrates will also be compared.     

High-isolation CPW MEMS shunt switches. 2. Design

For pt.1 see ibid., vol.48, no.6, p.1045-1052 (2000). In this paper, the second of two parts, the equivalent RLC model of the shunt switch is used in the design of tuned two- and four-bridge “cross” switches from 10 to 40 GHz. The cross switch attained an insertion loss of less than 0.3-0.6 dB, a return loss below -20 dB from 22 to 38 GHz in the up state, and a down-state isolation of 45-50 dB with only 1.5 pF of down-state capacitance (C_d). Also, an X-band microelectromechanical system (MEMS) switch with an insertion loss of less than 0.2 dB and an isolation of 35 dB is presented. This is done by inductively tuning the LC series resonance of the shunt switch. The MEMS bridge height is 1.5-2.5 μm, resulting in a pull-down voltage of 15-25 V. Application areas are in low-loss high-isolation communication and radar     

A DC-to-40 GHz four-bit RF MEMS true-time delay network

A monolithic true-time delay (TTD) network containing sixteen metal-to-metal contact RF microelectromechanical systems (MEMS) switches has been successfully fabricated and characterized. The TTD network was designed to produce flat delay time over a dc-to-40 GHz bandwidth with full 360-degree phase control at 22.5-degree intervals at 10.8 GHz. Measurements show a close match to the designed delay times for all sixteen switch states with 2.2 to 2.6 dB of insertion loss at 10 GHz. The worst group delay ripple in the dc-to-30 GHz range was 3 ps, well within the single bit delay time of 5.8 ps     

$Ka$-Band Low-Loss and High-Isolation Switch Design in 0.13-$mu{hbox {m}}$ CMOS

This paper presents designs and measurements of Ka-band single-pole single-throw (SPST) and single-pole double-throw (SPDT) 0.13-CMOS switches. Designs based on series and shunt switches on low and high substrate resistance networks are presented. It is found that the shunt switch and the series switch with a high substrate resistance network have a lower insertion loss than a standard designs. The shunt SPST switch shows an insertion loss of 1.0 dB and an isolation of 26 dB at >35 GHz. The series SPDT switch with a high substrate resistance network shows excellent performance with 2.2-dB insertion loss and isolation at 35 GHz, and this is achieved using two parallel resonant networks. The series-shunt SPDT switch using deep n-well nMOS transistors for a high substrate resistance network results in an insertion loss and isolation of 2.6 and 27 dB, respectively, at 35 GHz. For series switches, the input 1-dB compression point (1P₁) can be significantly increased to with the use of a high substrate resistance design. In contrast, of shunt switches is limited by the self-biasing effect to 12 dBm independent of the substrate resistance network. The paper shows that, with good design, several 0.13- CMOS designs can be used for state-of-the-art switches at 26-40 GHz.     

High-isolation W-band MEMS switches

This paper presents the design, fabrication and measurement of single, T-match and π-match W-band high-isolation MEMS shunt switches on silicon substrates. The single and T-match design result in -20 dB isolation over the 80-110 GHz range with an insertion loss of 0.25±0.1 dB. The π-match design results in a reflection coefficient lower than -20 dB up to 100 GHz, and an isolation of -30 to -40 dB from 75 to 110 GHz (limited by leakage through the substrate). The associated insertion loss Is 0.4±0.1 dB at 90 GHz. To our knowledge, this is the first demonstration of high-performance MEMS switches at W-band frequencies     

Novel high-isolation FET switches

This paper describes novel high-isolation monolithic microwave/millimeter-wave integrated circuit (MMIC) field-effect transistor (FET) switches that have higher isolation characteristics than conventional switches without much insertion loss degradation. The newly developed switches consist of series/shunt FETs and T-shaped R-C-R circuit. Each FET switch utilizes the parasitic capacitive component of the FETs in the off-state to produce a band-rejection filter at the operating frequency. The design method of the newly proposed switches and their characteristics are described herein. With this method, the isolation characteristics are improved by more than 15 dB between 5.4 GHz and 6.4 GHz and more than 20 dB between 5.5 GHz and 6.1 GHz over conventional values     

W-band CPW RF MEMS circuits on quartz substrates

This paper presents W-band coplanar waveguide RF microelectromechanical system (MEMS) capacitive shunt switches with very low insertion loss (-0.2 to -0.5 dB) and high-isolation (/spl les/ -30 dB) over the entire W-band frequency range. It is shown that full-wave electromagnetic modeling using Sonnet can predict the performance of RF MEMS switches up to 120 GHz. Also presented are W-band 0/spl deg//90/spl deg/ and 0/spl deg//180/spl deg/ switched-line phase shifters with very good insertion loss (1.75 dB/bit at 90 GHz) and a wide bandwidth of operation (75-100 GHz). These circuits are the first demonstration of RF MEMS digital-type phase shifters at W-band frequencies and they outperform their solid-state counterparts by a large margin.     

DCDC—20GHz射频MEMS开关

描述了 DC— 2 0 GHz射频 MEMS开关的设计和制造工艺 .开关为一薄金属膜桥组成的桥式结构 ,形成一个单刀单掷 (SPST)并联设置的金属 -绝缘体 -金属接触 .开关通过上下电极之间的静电力进行控制 ,其插入损耗及隔离性能取决于开态和关态的电容 .测试结果如下 :射频 MEMS开关驱动电压约为 2 0 V,在“开”态下 DC— 2 0 GHz带宽的插入损耗小于 0 .6 9d B;在“关”态下在 14— 18GHz时隔离大于 13d B,在 18— 2 0 GHz时隔离大于 16 d B.本器件为国内首只研制成功的宽带射频 MEMS开关     

A compact V-band 2-bit reflection-type MEMS phase shifter

Air-gap overlay CPW couplers and low-loss series metal-to-metal contact microelectromechanical system (MEMS) switches have been employed to reduce the loss of reflection-type MEMS phase shifters at V-band. Phase shift is obtained by changing the lengths of the open-ended stubs using series MEMS switches. A 2-bit [135] reflection-type MEMS phase shifter showed an average insertion loss of 4 dB with return loss better than 11.7 dB from 50 to 70 GHz. The chip is very compact with a chip size as small as 1.5 mm /spl times/ 2.1 mm.     

Frequency Scalable Model for MEMS Capacitive Shunt Switches at Millimeter-Wave Frequencies

This paper presents an approach to RF microelectromechanical systems (MEMS) capacitive shunt switch design from $K$-band up to $W$-band based on the scalability of the RF MEMS switch with frequency. The parameters of the switch's equivalent-circuit model also follow scaling rules. The measurement results of the fabricated switches show an excellent agreement with simulations that allow to validate the MEMS model in the entire band from 20 up to 94 GHz. This model is going to be used in the phase shifter circuit design for antenna array applications. The first 60-GHz phase shifter results are also reported here.      

高隔离度宽频段组合式RF-MEMS开关的设计

接触式与电容耦合式两类RF MEMS开关各自在一定的频段内,都具有较高的隔离度,但仍然很难满足微波控制系统中对高隔离度的要求.为了获得全波段高隔离度RF MEMS开关,单元开关很难达到要求,在此目标要求下,提出了组合式RF MEMS开关的设计,分别利用HFSS软件对各单元进行结构参数优化,再将两者集成在一起,得到的组合式RF MEMS开关,这种组合式开关在0～20 GHz时隔离度都高于-60 dB,在(≤5 GHz),隔离度高于-70 dB,这是一般单元开关及其他半导体固态开关所无法企及的,而且,在DC～20 GHz范围内,开关的插入损耗小于-0.20 dB,而且并没因隔离度的提高,牺牲了插入损耗.     

一种DC～5GHz串联微波开关的温度特性和功率处理能力的测试与分析

描述了一种串联微波MEMS开关的设计、制造过程,它制作在玻璃衬底上,采用金铂触点,在DC～5GHz,插损小0.6dB,隔离度大于30dB,开关时间小于30μs.对这种微波开关的温度特性和功率处理能力进行了测试,在DC～4GHz,85℃下的插损增加了0.2dB,-55℃下的插损增加了0.4dB,而隔离度基本保持不变.在开关中流过的连续波功率从10dBm上升到35.1dBm,开关的插损下降了0.1～0.6dB,并且在35.1dBm(3.24W)下开关还能工作.和所报道的并联开关最大处理功率(420mW)相比,该结果说明串联开关具有较大的功率处理能力.