This publication deals with the design of carbon nanotubes (CNT) based nano-electromechanical system (NEMS)
consisting in a variable capacitor working at microwave frequencies. This device is based on an array of moveable CNT
cantilever electrostatically actuated over a ground plane (figure 1 and 2). To design this component, a time-efficient
numerical algorithm for the prediction of CNT electromechanical behavior has been developed. This numerical tool
permits to calculate the pull-in voltage and flexion of the CNT's tip for various devices' parameters like CNT's diameter
and length, initial air gap (g) ... Our software also takes into account the Van der Waals (VdW) forces and the fringing
field effects. The results demonstrate that, unlike for RF-MEMS, fringing field effects are preponderant for CNT-based
This paper also discusses on the accuracy of the developed software. In order to validate our prediction, we used
finite element simulation software : COMSOL® and experimental results found in literature and compare them to our
prediction. Results prove that we obtain, for a decrease of the simulation time by two orders of magnitude, a maximum
error on the pull-in voltage of 7% for various kinds of structures and dimensions.
These results were finally used for the design of NEMS demonstrators. The microwave behavior of the varactors,
over a large range of frequency, is presented. Simulations with 3D finite-element-method electromagnetic software were
performed to optimize the structure and predict its microwave performances, which conclude the design of our
microwave carbon nanotubes (CNT) based nano-electromechanical system (NEMS) variable capacitor.
This paper deals with the development of a micro-interconnection technology suitable for the elaboration of RF-NEMS
(Nano-ElectroMechanical Systems) varactors. It aims to present an extension of RF MEMS concept into nano-scale domain
by using multi-walled carbon nanotubes (MWCNT) as movable part instead of micrometric membranes into reconfigurable
passive circuits for microwave applications.
For such a study, horizontal configuration of the NEMS varactors has been chosen and is commented. The technology is
established to fulfill several constraints, technological and microwave ones.
As far as technological requirements are concerned, specific attentions and tests have been carried out to satisfy:
• Possible and later industrialization. No e-beam technique has been selected for RF NEMS varactor elaboration.
Lateral MWCNT growth performed on a Ni catalyst layer, sandwiched between two SiO2 layers, showed
feasibility of suspended MWCNT beam.
• High thermal budget, induced by the MWCNT growth by CVD (Chemical Vapor Deposition), at least to 600°C.
All the dielectric and metallic layers, required to interlink the nano world with the micrometric measurements one,
have been studied accordingly. Consequently, the order of the technological steps has been identified.
About microwave and actuation specifications (targeted close to 25V), the minimization of losses and actuation voltage
implies large layer's thicknesses compared to the CNT diameter.
Several specific technological issues are presented in this paper, taking care of both technological and microwave
compatibility to go toward RF NEMS varactor's elaboration.
This paper introduces the use of germanium as resistive material in RF MicroElectroMechanical (MEMS)
devices. Integrated resistors are indeed highly required into RF MEMS switches, in order to prevent any RF
signal leakage in the bias lines and also to be compatible with ICs.
Germanium material presents strong advantages compared to others. It is widely used in microtechnologies,
notably as an important semi-conductor in SiGe transistors as well as sacrificial or structural layers and also
mask layer in various processes (Si micromachining especially). But it also presents a great electrical
characteristic with a very high resistivity value. This property is particularly interesting for the elaboration of
integrated resistors for RF components as it assures miniaturised resistors in total agreement with
Its compatibility as resistive material in MEMS has been carried out. Its integration in the entire MEMS process
has been fruitfully achieved and led to the successful demonstration and validation of integrated Ge resistors into
serial RF MEMS variable capacitors, without any RF perturbations.
In this paper, capacitive RF-MEMS switches topologies are investigated regarding their power handling
capabilities. The topologies differ from the ability to handle thermal stress by an optimization of their anchorage arms.
A specific meander arms design leads in fact to enhance by a decade the flexibility regarding their thermal expansion.
To evaluate the proposed RF-MEMS morphology, a specific thermal stress protocol has been defined and applied from
20°C up to 120°C. The monitoring of air gap, actuation voltage and insertion losses has been performed after each
thermal stress in order to check the impact of the temperature on working switch. The main result indicates that a
different thermal behavior depending on the MEMS anchorage arms morphology has been obtained.
Miniaturization, low cost and excellent performances at microwave and millimeterwave applications represent the main leitmotivs of the future mass market communication systems. Consequently, a novel "MEMS above IC" technology has developed in order to allow the elaboration of post-processed micro-machined passive components on top of SiGe circuits to realize a complete short-range communication receiver centered at 24 GHz.
The developed technology is based on the use of : -a thick organic layer (BCB), which is employed as a dielectric membrane,
-metallizations to realize the passive metal layer and also the vias to interconnect the active circuits with the post-processed passive components, -and a bulk silicon micromachining.
This 'above IC' technology presents many advantages, as it uses conventional equipments of microelectronics and is in adequation with high frequency applications. A specific attention has been carried out in order to assure the compatibility of the post-process steps and the IC’s. This has been performed through the choice of the adequate technological steps, which had to present a low temperature budget. The compatibility of each step has been evaluated with a specific test protocol on SiGe transistors. It implies static and dynamic characterisation of these transistors as well as low frequency noise measurements. Each step has been validated, even the bulk silicon micromachining. Design rules have thus been defined in order to localize the silicon etching without any damage on the ICs.
We present an original RF-MEMS switch topology associated with an efficient design methodology. The proposed switch has been optimized thank to a scalable electrical model, fabricated and measured and exhibits isolations better than -23 dB and losses less than 0.25 dB at 24 GHz for a pull down voltage of 22V. The proposed topology and design methodology can then be efficiently used to optimize more complex RF-MEMS with enhanced microwave performances.
This paper reports on the investigation of the potentialities of the MEMS technologies to develop innovative microsystem for millimetre wave communication essentially for space applications. One main issue deals with the robustness and the reliability of the equipment as it may difficult to replace or to repair them when a satellite has been
launched. One solution deals with the development of redundancy rings that are making the front end more robust. Usually, the architecture of such system involves waveguide or diode technologies, which present severe limitations in term of weight, volume and insertion loss. The concept considered in this paper is to replace some key elements of such system by MEMS based devices (Micromachined transmission lines, switches) in order to optimize both the weight and
the microwave performance of the module. A specific technological process has been developed consisting in the fabrication of the devices on a dielectric membrane on air suspended in order to improve the insertion loss and the isolation. To prove the concept, building
blocks have been already fabricated and measured (i.e micromachined transmission and filter featuring very low insertion loss, single pole double through circuits to address the appropriate path of the redundancy ring). We have to outline that MEMS technology have allowed a simplification of the architecture and a different system partitioning which gives more degree of freedom for the system designer. Furthermore, it has been conducted an exhaustive
reliability study in order to identify the failure mechanisms. Again, from the results obtained, we have proposed an original topology for the SPDT circuit that takes into account the reliability behaviour of the MEMS devices and that allow to prevent most of the failure mechanisms reported so far (mainly related to the dielectric charging effect). Finally, the active device (millimetre wave low noise amplifier) will be reported on the MEMS based chip using flip
chip technology to integrate the Microsystem.
Because of their interesting electrical, mechanical and thermal properties at high frequencies, polymers are becoming more and more attractive in the development of RF and millimeterwave applications. Their process ease and characteristics indeed permit improvement in the performance of passive components as well as their integration especially with active devices. Investigated in this paper are a few technological solutions based on the use of thick polymer layers. The first one consists of a thick organic layer that may be employed as a dielectric membrane on bulk silicon micromachined substrates in order to realize suspended components, which exhibit thus very low losses and dispersion on a large frequency range. The elevation of passive circuits through thick polymers represents another attractive solution to minimize the losses induced by the silicon substrate, which through a low thermal budge provides a particularly attractive method for post-processing over active devices. The use of polymers for additional surface micromachining into coplanar slots on silicon substrates can also improve both losses and quality factor. Finally, an application using a thin polymer layer as dielectric protection for a MEMS device is described.
This paper presents a new silicon technology that is used for innovative components such as a MicroElectroMechanical Systems for microwave and millimeter-wave applications. This technology is based on two different bulk and surface silicon micro- machining processes. The former one, the bulk micro-machining, is well fitted to the realization of low loss microwave circuits suspended on a thin membrane, whereas the surface one allows the realization of actuable devices. This confers to the structure an interesting MEM behavior particularly important in millimeter- wave applications. As a demonstration of the advantage of combining surface and bulk micromachining a low loss (< 0.1 dB at 100 GHz), high isolation (approximately equals 30 dB at 10 GHz) capacitive switch has been designed, processed and measured. A distributed switch with enhanced performance has also been investigated.
A new fully silicon MEM technology and design methodology is introduced to realize millimeter-wave applications such as switches. It is based on two kinds of micro-machining techniques: a bulk micro-machines used to realize micro-wave circuits on a suspended membrane in order to decrease losses, and a surface micro-machining to make air-bridges actuable by electrostatic force. A MEM bridge electrical model has been investigated and implemented in the design of distributed switches.