Assessment of dielectric charging in electrostatically driven MEMS devices: A comparison of available characterization techniques

The present work investigates the results of different characterization methods for the dielectric charging phenomenon applicable to metal–insulator–metal (MIM) capacitors and electrostatically actuated micro-electro-mechanical-systems (MEMS). The discharge current transients (DCT), thermally stimulated depolarization current (TSDC) and Kelvin probe force microscopy (KPFM) assessment methods have been applied to either MIM capacitors or electrostatic capacitive MEMS switches or both. For the first time, the KPFM methodology has been used to create a link between the results obtained from the DCT and TSDC techniques applicable for MIM and the results from MEMS switches. The comparison shows that the application of KPFM method to MIM and MEMS leads to the same results on the electrical properties of the dielectric material. This provides a novel powerful tool for the assessment of dielectric charging for MEMS switches using MIM capacitors which have much simpler layer structure. On the other hand the TSDC method reveals a continuous distribution of relaxation time constants, which supports the dependence of relaxation time constant calculated for MEMS on the duration of the observation time window.     

Effect of deposition conditions on charging processes in SiNx: Application to RF-MEMS capacitive switches

The paper presents a systematic investigation of dielectric charging in low temperature silicon nitride for RF-MEMS capacitive switches. The dielectric charging is investigated with the aid of Metal-Insulator-Metal (MIM) capacitors with different thickness dielectric film and symmetric and asymmetric metal contacts. The experimental results demonstrate that the charging process is almost symmetric in low temperature deposited silicon nitride. Experiments performed in both MIM and MEMS reveal that the charging process is strongly affected by temperature. Specifically at high temperatures the charging rate increases exponentially with temperature.     

Determination of bulk discharge current in the dielectric film of MEMS capacitive switches

The present work presents a new method to calculate the discharge current in the bulk of dielectric films of MEMS capacitive switches. This method takes into account the real MEMS switch with non uniform trapped charge and air gap distributions. The assessment of switches with silicon nitride dielectric film shows that the discharge current transient seems to obey the stretched exponential law. The decay characteristics depend on the polarization field’s polarity, a fact that comes along with experimental results obtained from the thermally stimulated depolarization currents (TSDC) method used in MIM capacitors.     

Charging-Effects in RF capacitive switches influence of insulating layers composition

The dielectric charging is one of the major failures reducing the reliability of capacitive switches with electrostatic actuation. Then the control of the charging/discharging processes is a key factor to allow a fast recovering of the dielectric after charging. From transient current measurements on MIM capacitors it is possible to select the best material for RF-MEMS.We have studied different PECVD silicon nitride obtained under low (380 KHz), high (13.56 MHz) or mixed (380kHz/13.56MHz) frequency power supply. The conduction mechanism into the dielectrics has been deduced from current measurements on MIM capacitors. Then the film properties have been studied by infrared measurement in order to identify the chemical bond into the dielectric which can explain the charging behaviour. It was observed that low hydrogen content in the films is in good correlation with electrical quality and kinetic of the charging/discharging processes.     

On the reliability of electrostatic NEMS/MEMS devices: Review of present knowledge on the dielectric charging and stiction failure mechanisms and novel characterization methodologies

This paper reviews the state of the art knowledge related to critical failure mechanisms in electrostatic micro- and nano-electromechanical systems (MEMS and NEMS) which are the dielectric charging and stiction. It describes also the recent employed nanoscale characterization techniques for these phenomena based on Kelvin probe force microscopy (KPFM) and force–distance curve measurements. The influence of relative humidity and dielectric deposition conditions on the charging/discharging processes is discussed. Moreover, different stiction mechanisms induced by electrostatic force and/or meniscus formation are analyzed. Finally, novel characterization methods are presented and used to correlate between the results from MEMS devices and metal–insulator–metal (MIM) capacitors. These methods are employed in view of application in electrostatic capacitive MEMS switches and could be easily extended to explore other NEMS/MEMS devices. The study provides an accurate understanding of the charging and stiction related failure mechanisms, presents guidelines for a proper packaging environment, and reveals precise explanations for the literature reported device level measurements of electrostatic MEMS devices.     

Modeling of dielectric charging in electrostatic MEMS switches

The most important failure mechanism for electrostatic MEMS switches is dielectric charging, which contributes to a significant reduction of the device lifetime. In this study the correlation between the dielectric properties and the switch lifetime is evaluated. The conduction mechanism and trapping kinetics for two types of PECVD SiN_x are determined by I–V sweeps and constant-current injections from Metal–Insulator–Metal (MIM) capacitors. This type of procedure is used as a basis for modeling the charge build-up in a switch. Despite significant differences between the dielectrics, in terms of leakage current and trapping properties, the numerical model of charge build-up fits well with experimental data. We conclude that the switch lifetime can be correlated with the trapping properties of the dielectric itself.     

BST-MEMS移相器开关

为了提高MEMS电容开关性能,介绍了移相器的一种新型结构——分布式电容周期性加载结构。分析发现移相器的相移度和单元可变电容的变化率有关。目前MEMS可变电容单元采用的介质基本上是氮化硅。BST薄膜作为一种性质优良的介电材料,其介电常数远大于氮化硅。从MEMS移相器开关性能的几个关键指标出发,探讨在MEMS移相器开关中,用BST薄膜代替氮化硅介质的可能性。     

无机介质集成薄膜电容的制备研究

以Cr/Ag/Cr金属膜系为电极,电子束蒸发镁橄榄石(2MgO·SiO2)膜为绝缘介质,在陶瓷基片(表面较粗糙)上制备了MIM结构无机集成薄膜电容。光学显微镜和扫描电镜分析显示,电容的绝缘强度和介电性能主要取决于介质膜致密程度。沉积后适当的热处理有助于改善电容性能,但过度的热处理却可能导致由晶化和扩散引起的负面作用。所得电容击穿场强达到了107V/m以上,5MHz频率tanδ为0.01。     

Nanostructured metal–insulator–metal capacitor with anodic titania

This paper presents fabrication and electrical characterization of barrier type TiO₂ metal–insulator–metal (MIM) capacitor using anodization. Polarization process, conduction mechanisms, and structural properties are studied in detail. We found that the anodization voltage played a major role in electrical and structural properties of the thin film. The barrier type anodic TiO₂ is suggested as a dielectric material for high-performance MIM capacitors.     

Effect of size and plasma treatment and the application of Weibull distribution on the breakdown of PECVD SiNx MIM capacitors

The dielectric breakdown field is one of the important concerns for device reliability. The breakdown of dielectric is originated at a fatal flaw that grows to cause failure and can be explained by the weakest-link theory. In this study, metal-insulator-metal (MIM) capacitors with plasma enhanced chemical vapor deposited (PECVD) SiN_x are prepared. Ammonia (NH₃) plasmas are applied after the deposition of the dielectric SiN_x. The Weibull distribution function, which is based on the weakest-link theory, is employed to analyze the effect of the electrode area as well as the plasma treatment on the breakdown of the MIM capacitors. The time dependent dielectric breakdown testing indicates a decrease in both the leakage current and the lifetime of the MIM capacitors treated with plasma. Possible dielectric degradation mechanisms are explored.     

开关线型四位数字MEMS移相器

介绍了一种基于射频微机械串联开关设计的开关线型四位数字微机电系统(M icro-e lectrom echan ica lSystem s以下简称M EM S)移相器。该移相器集成了16个RF M EM S开关,使用了13组四分之一波长传输线和M IM接地耦合电容,有效地使开关的驱动信号和微波信号隔离,串联容性开关设计有效地降低了开关的启动电压。使用低温表面微机械工艺在360μm厚的高阻硅衬底上制作移相器,芯片尺寸4.8 mm×7.8 mm。移相器样品在片测试结果表明,频点10.1 GH z,22.5°相移位的相移误差为±0.4,°插损2.8 dB;45°位的相移误差为±1.1,°插损2.0 dB;在X波段,对16个相移态的测试结果表明,移相器的插入损耗小于4.0 dB,驻波比小于2.4,开关驱动电压为17~20 V。     

Lanthanide (Tb)-doped HfO/sub 2/ for high-density MIM capacitors

A high-density metal-insulator-metal (MIM) capacitor with a lanthanide-doped HfO/sub 2/ dielectric prepared by physical vapor deposition (PVD) is presented for the first time. A significant improvement was shown in both the voltage coefficient of capacitance (VCC) and the leakage current density of MIM capacitor, yet the high capacitance density of HfO/sub 2/ dielectrics was maintained by achieving the doping of Tb with an optimum concentration in HfO/sub 2/. This technique allows utilizing thinner dielectric film in MIM capacitors and achieving a capacitance density as high as 13.3 fF//spl mu/m/sup 2/ with leakage current and VCC values that fully meet requirements from year 2005 for radio frequency (RF) bypass capacitors applications.     

Electrical characteristics and reliability of UV transparent Si/sub 3/N/sub 4/ metal-insulator-metal (MIM) capacitors

In this paper, we discuss the electrical characteristics and reliability of UV transparent Si/sub 3/N/sub 4/ metal-insulator-metal (MIM) capacitors. We examine film thicknesses in the range of 55 to 25 nm with capacitance densities from 1.2 ff//spl mu/m/sup 2/ to 2.8 ff//spl mu/m/sup 2/, respectively, for single MIM capacitors. A new approach for projecting the dielectric reliability of these films extends the limits of maximum operating voltage. Accounting for temperature acceleration and area scaling, the projected lifetimes can be met for a wide range of operating conditions.     

Structural, electrical and optical properties of GZO/HfO2/GZO transparent MIM capacitors

Metal–insulator–metal (MIM) transparent capacitors were prepared by pulsed laser deposition (PLD) on glass substrates. The effect of the thickness of the dielectric layer and oxygen pressure on structural, electrical, and optical properties of these capacitors was investigated. Experimental results show that film thickness and oxygen pressure have no effect on the structural properties. It is also found that the optical properties of the HfO₂ thin films depend strongly on both the film thickness and oxygen pressure. The electrical properties of transparent capacitors were investigated at various thickness of the dielectric layer. The capacitor shows an overall high performance, such as a high dielectric constant of 28 and a low leakage current of 2.03×10⁻⁶ A/cm² at ±5 V. Transmittance above 70% was observed in visible region.     

A high performance MIM capacitor using HfO2 dielectrics

Metal-insulator-metal (MIM) capacitors with a 56 nm thick HfO₂ high-κ dielectric film have been fabricated and demonstrated for the first of time with a low thermal budget (~200°C). Voltage linearity, temperature coefficients of capacitance, and electrical properties are all characterized. The results show that the HfO₂ MIM capacitor can provide a higher capacitance density than Si₃N₄ MIM capacitor while still maintaining comparable voltage and temperature coefficients of capacitance. In addition, a low leakage current of 2×10^-9 A/cm² at 3 V is achieved. All of these make the HfO ₂ MIM capacitor to be very suitable for use in silicon RF and mixed signal IC applications     

High-Performance MIM Capacitors Using HfLaO-Based Dielectrics

Metal-insulator-metal (MIM) capacitors fabricated with (8%) La-doped HfO₂ single layer as well as HfLaO/ LaAlO₃/HfLaO multilayer dielectric stack are demonstrated. While the La-doped HfO₂ single layer is crystallized at 420^°C annealing, HfLaO/LaAlO₃/HfLaO multilayer dielectric stack remains amorphous. A high dielectric-constant value of 38 can be obtained when 8% La-doped HfO₂ is crystallized into cubiclike structure. However, it is observed that the linearity of MIM capacitor is degraded upon crystallization. The multilayer film has lower average dielectric constant but shows low quadratic voltage linearity of less than 1000 ppm/V² up to a capacitance density of 9 fF/?m² . It is observed that the HfLaO single-layer MIM is suitable for the applications with requirements of high capacitance density and robust reliability, while the multilayer MIM is suitable for a precision circuit.     

静电式RF MEMS开关的可靠性

MEMS开关是最常见的RF MEMS控制元件,是RF结构中一个关键的MEMS器件。长期可靠性是目前制约MEMS开关商业化进程中的一个主要问题。主要综述了静电式RF MEMS开关可靠性的新进展。欧姆式开关通常由于黏附或接触电阻的增大而失效,电容式开关的主要失效机理则与电介质层的充电有关。接触材料的选择是决定欧姆开关可靠性最重要的一个因素,"主动断开/被动接触"MEMS开关适用于软金属材料欧姆接触的可靠性要求。改善电容式开关可靠性的途径是改善介电层、优化驱动电压波形等以减小介质层的充电。     

Tunable bandstop MEMS filter for millimetre-wave applications

The design and realisation of original millimetre-wave tunable bandstop filters using MEMS (micro-electro-mechanical-systems) technology for millimetre-wave applications is presented. The tunable behaviour is achieved by using MEMS switches. The overall structures, including the MEMS switches, have been manufactured using dielectric membrane in order to minimise the dielectric losses. Experimental validations are reported and validate the proposed topology: the bandstop frequency is shifted by approximately 3.5 GHz in V-band when the switches are actuated     

Very high-density (23 fF//spl mu/m/sup 2/) RF MIM capacitors using high-/spl kappa/ TaTiO as the dielectric

A very high density of 23 fF//spl mu/m/sup 2/ has been measured in RF metal-insulator-metal (MIM) capacitors which use high-/spl kappa/ TaTiO as the dielectric. In addition, the devices show a small reduction of 1.8% in the capacitance, from 100 kHz to 10 GHz. Together with these characteristics the MIM capacitors show low leakage currents and a small voltage-dependence of capacitance at 1 GHz. These TaTiO MIM capacitors should be useful for precision RF circuits.     

Measurement and analysis of substrate leakage current of RF mems capacitive switches

This paper focused on a new direction of study on leakage current called substrate charge injection. The substrate leakage current of capacitive RF micro-electro-mechanical-system (MEMS) switches was measured, and the conduction mechanism was estimated. The study of the leakage current conduction mechanisms of the substrate dielectric film shows that leakage is mainly induced by hopping conduction at low electric fields, whereas both Schottky emission and hopping conduction may contribute to the leakage current at high fields. The quantitative relationship between the substrate leakage current and the dielectric layer leakage current was also determined for the first time. In the case of low drive voltage (0–30 V), the substrate leakage current significantly contributes to the total leakage current. Results show that the charging properties of the substrate should not be neglected at low drive voltage because such properties could significantly affect the functionality and reliability of RF MEMS switches.