E. Martincic

Copper micromoulding process for NMR microinductors realization

Abstract Micromoulding has been used to realize high quality factor microcoils operating at room temperature for NMR application. The mould is a positive thick resist (AZ 4562) and the electrodeposition process is optimized for copper structures. Two types of micromoulding processes were performed: conventional one using binary mask, and gray-tone lithography one in order to control the local thickness of the metallic device by controlling current density repartition. The copper growth is simulated with the two types of mould and the realization is consistent with expected results, i.e. the thickness of different structures can be modified using the second process. A variation of about 10% between the highest and the lowest thickness is obtained for a 200xa0μm device size with a mean thickness of 3.5xa0μm. Classical copper micromoulding is used to obtain nuclear magnetic resonance (NMR) imagery antennas in the range of 500xa0kHz–1xa0GHz. Five turns coils (line width 400xa0μm, space width 300xa0μm, thickness 7xa0μm) are realized on each side of glass and kapton™ substrates. First measurements at ambient temperature show, respectively resonant frequencies of 174 and 102xa0MHz, and Q factors of 74 and 60.

Optimization and Microfabrication of High Performance Silicon-Based MEMS Microspeaker

A novel structure of electrodynamics microelectromechanical systems (MEMS) microspeaker designed for mobile electronics is proposed in this paper. The originality of the device lies on the use of a rigid silicon membrane suspended by highly flexible silicon springs, contrary to most MEMS and non-MEMS microspeakers, which use polymer diaphragms. Important rigidity of the membrane and high linearity of the magnetic actuation conferred outstanding sound quality. The design of the silicon springs enabled large out-of-plane displacement of the membrane, which improved the bass rendering and the acoustic intensity over the whole bandwidth. The low density of silicon material helped to reduce the mobile mass and thus improved the microspeaker efficiency. A prototype with a membrane diameter of 15 mm and a thickness of 20 μm is microfabricated and characterized. The silicon springs enabled out-of-plane displacement of more than 300 μm. Acoustic intensity of 80-dB SPL is measured at 10 cm with 500-mW input power. This sound pressure level is obtained at frequencies from 330 Hz up to 70 kHz. Thanks to the membrane backside microstructure, most of the membrane proper modes are shifted out of the audible bandwidth. The measured electroacoustic efficiency is almost three times better than that of conventional microspeakers.

Linear and non linear behavior of mechanical resonators for optimized inertial electromagnetic microgenerators

In this work, the design, fabrication and characterization of an electromagnetic inertial microgenerator compatible with Si micro-systems technology is presented. The device includes a fixed micromachined coil and a movable magnet mounted on a resonant polymeric structure. The characterization of the fabricated prototypes has allowed to observe the presence of non-linear effects that lead to the appearance of hysteretic vibrational phenomenon and strongly affect the output of the microgenerator. These effects are likely related to the mechanical characteristics of the polymeric membrane, and determine an additional dependence of vibration frequency on the excitation amplitude. Under such non-linear conditions, power densities up to 40xa0μW/cm3 are obtained for devices working with low level excitation conditions similar to those present in domestic and office environment.

Electromagnetic micro-device realized by electrochemical way

Abstract In this paper, realization process and electroplated copper and permalloy properties are presented in order to fabricate micro-coils. RF electrical and magnetic characterizations of the first devices with 40 turns obtained for low frequencies application are exposed showing an inductive behavior under 220xa0MHz ( L =320xa0nH) and a capacitive behavior above. Experimental results are compared with calculations. A comparative magnetic field measurement is performed using micro-coils and AMR.

Magnetic micro-transformers realized with a flip-chip process

Micromachined transformers are complex devices. Conductors, insulators and magnetic materials are manufactured on the same substrate, thus leading to transformer structures often with many manufacturing levels. We describe here a new low cost solution to make quasi-planar transformer structures. The primary and secondary coils are manufactured separately and assembled by flip-chip technology. This novel structure allows a single conductor level process. The influence of different parameters of the design on expected performances is discussed. A set of transformers was made with 1 µm thick Al conductors to assess the process validity. First measurements were carried out. A current mode operation was tested and showed an output voltage proportional to the operation frequency up to 10 MHz. Tests were carried out under no-load conditions and with resistive load (1 kΩ and 470 Ω values). A resonance mode appeared for frequency above 15 MHz but was not measured.

Fabrication and characterization of flexible pressure sensor arrays made by film transfer technology

This paper presents an efficient and reproducible fabrication process of flexible-substrate-based pressure sensor arrays, using a technology of film transfer which has been recently developed in our laboratory [1]. The sensors are composed of two millimetric copper electrodes, separated by a polydimethylsiloxane (PDMS) dielectric layer, the operation of which is based on a capacitance change induced by an applied force. Sensor arrays were fabricated on two types of substrate: a rigid substrate (glass) used for the validation of the fabrication process, and a flexible substrate (Kapton) used to realize the wanted flexible sensors. Regarding the flexible arrays, a very small curvature radius is possible without any damage to the sensors. Six three-by-three sensor arrays were fabricated. They feature capacitances ranging from 3.45 pF to 14.40 pF, according to their dimensions. The discrepancy between the capacitances within each array is quite low (standard deviation is less than 7 % of the mean value). The sensitivity of the considered on-glass samples is around 80 pF/mN under 2N loading conditions.

Experimental study of PDMS mechanical properties for the optimization of polymer based flexible pressure micro-sensors

This paper reports on the optimization of flexible PDMS-based normal pressure capacitive micro-sensors dedicated to wearable applications. The deformation under a normal force of PDMS thin films of thicknesses ranging from 40 μm to 10 mm is firstly experimentally studied. This study points out that for capacitive micro-sensors using bulky PDMS thin films as deformable dielectric material, the sensitivity to an applied normal load can be optimized thanks to an adequate choice of the so-called form ratio of the involved PDMS thin film. Indeed, for capacitive micro-sensors exhibiting 9 mm2 electrodes, the capacitance change under a 6 N load can be adjusted from a few percent up to over 35% according to the choice of the load-free thickness of the used PDMS film. These results have been validated thanks to electromechanical characterizations carried out on two flexible PDMS based capacitive normal pressure micro-sensor samples fabricated with two different thicknesses. The obtained results open the way to the enhanced design of PDMS based pressure sensors dedicated to wearable and medical applications. Further works will extend this study to a wider range of sensor dimensions, and using numerical modelling.

Development of an elementary micromachined electromagnetic digital actuator for microdisplacements

In this paper an elementary micromachined digital electromagnetic actuator for microdisplacements is presented. The moving part is composed of a permanent magnet placed in a silicon square cavity. This magnet can reach 4 discrete positions and can be switched by applying current pulses through wires placed below the cavity. A semi-analytical model has been developed to design the actuator. A prototype, composed of a silicon part, has been manufactured using Deep Reactive Ion Etching (DRIE) process. The device has been characterized by several performance tests: the response time is 8 ms and the measured stroke is 179 μm.

Design of a long range bidirectional MEMS scanner for a tunable 3D integrated Mirau interferometer

Mirau interferometers are two beam interferometers with coaxial optical beams that are widely used in full-field optical surface profilers. An integrated Mirau interferometer with a MEMS mirror scanner is proposed in this paper. The novelty of the scanner design is the use of self-aligned vertical electrostatic combs made in double SOI wafer technology which allows a large range, bidirectional, and symmetric vertical translation of the reference mirror. Electrostatic and mechanical analytical calculations and Finite Element Modeling simulations were carried out to design and optimize the MEMS scanner. A large bidirectional range (+/-20 μm) motion under 60V applied voltage is achievable. Good flatness of the reference mirror is preserved during motion, what is essential for interferometrie measurements. A fabrication process which minimizes the number of mask levels is proposed. It is based on front and back side Deep Reactive Ion Etching and dry film photoresist lithographic steps.

Non-invasive capacitive pressure sensor: Microfabrication process and first electro-mechanical characterization

Kapton-based flexible pressure sensor arrays are fabricated using a new technology of film transfer. The sensors are dedicated to the non-invasive measurement of pressure/force in robotic, sport and medical applications. The sensors are of a capacitive type, and composed of two millimetric copper electrodes, separated by a polydimethylsiloxane (PDMS) deformable dielectric layer. On the flexible arrays, a very small curvature radius is possible without any damage to the sensors. The inhomogeneity of the capacitances in array is quite low (deviation of ±7% compared to the average value). The process is accurate and reproducible (transfer yield of 100%). The electrical characterization is also presented. In the preliminary electro-mechanical characterization, a sensor (with a PDMS dielectric layer of 660 μm thickness and a free load capacitance of 480 fF) undergoes a capacitance change of 17% under a 300 kPa normal stress.