A magneto-mechanical accelerometer based on magnetic tunnel junctions

Accelerometers have widespread applications and are an essential component in many areas such as automotive, consumer electronics and industrial applications. Most commercial accelerometers are based on micro-electromechanical system (MEMS) that are limited in downscaling and power consumption. Spintronics-based accelerometers have been proposed as alternatives, however, current proposals suffer from design limitations that result in reliability issues and high cost. Here we propose spintronic accelerometers with magnetic tunnel junctions (MTJs) as building block, which map accelerations into a measurable voltage across the MTJ terminals. The device exploits elastic and dipolar coupling as a sensing mechanism and the spintronic diode effect for the direct read out of the acceleration. The proposed technology represents a potentially competitive and scalable solution to current capacitive MEMS-based approaches that could lead to a step forward in many of the commercial applications.Comment: main document with 4 figures + supplemental informatio

A mixed-signal control system for Lorentz-force resonant MEMS magnetometers

This paper presents a mixed-signal closed-loop control system for Lorentz force resonant MEMS magnetometers. The control system contributes to 1) the automatic phase control of the loop, that allows start-up and keeps self-sustained oscillation at the MEMS resonance frequency, and 2) output offset reduction due to electrostatic driving by selectively disabling it. The proposed solution proof-of-concept has been tested with a Lorentz force-based MEMS magnetometer. The readout electronic circuitry has been implemented on a printed circuit board with off-the-shelf components. Digital control has been implemented in an FPGA coded with VHDL. When biased with 1 V and a driving current of 300 µArms, the device shows 9.75 pA/µT sensitivity and total sensor white noise of 550 nT/vHz. Offset when electrostatic driving is disabled is 793 µT, which means a 40.1% reduction compared when electrostatic driving is enabled. Moreover, removing electrostatic driving does not worsen bias instability, which is lower than 125 nT in both driving cases.Peer ReviewedPostprint (published version

A CubeSAT payload for in-situ monitoring of pentacene degradation due to atomic oxygen etching in LEO

This paper reports and discusses the design and ground tests of a CubeSat payload which allows to measure, in-situ and in real time, the degradation of a polymer of electronic interest due to atomic oxygen etching in LEO. It provides real-time information on how the degradation occurs, eliminating the need to work with samples recovered once the mission has finished. The polymer, TIPS-Pentacene, is deposited on the surface of a microelectromechanical (MEMS) cantilever, which works as a resonator embedded in a Pulsed Digital Oscillator circuit. The mass losses in the polymer due to atomic oxygen corrosion produce variations in the resonant frequency of the MEMS, which is continuously sensed by the circuit and transmitted to the ground. This way, polymer mass losses around 10-12 kg can be detected during the mission. The payload is a part of the 3Cat-1 mission, a nano-satellite aimed at carrying out several scientific experiments.Peer ReviewedPostprint (author's final draft

A Stable Optical Trap from a Single Optical Field Utilizing Birefringence

We report a stable double optical spring effect in an optical cavity pumped with a single optical field that arises as a result of birefringence. One end of the cavity is formed by a multilayer Al$_{0.92}$Ga$_{0.08}$As/GaAs stack supported by a microfabricated cantilever, with a natural mode frequency of $274$ Hz. The optical spring shifts the resonance to $21$ kHz, corresponding to a suppression of low frequency vibrations by a factor of more than $10^{4}$. The stable nature of the optical trap allows the cavity to be operated without any external feedback and with only a single optical field incident

Microelectromechanical Isolation of Acoustic Wave Resonators

Microelectromechainical systems (MEMS) is a rapidly expanding field of research into the design and fabrication of actuated mechanical systems on the order of a few micrometers to a few millimeters. MEMS potentially offers new methods to solve a variety of engineering problems. A large variety of MEMS systems including flip-up platforms, scanning micromirrors, and rotating micromirrors are developed to demonstrate the types of MEMS that can be fabricated. The potential of MEMS for reducing the vibration sensitivity of surface acoustic wave and surface transverse wave resonators is then evaluated. A micromachined vibration isolation system is designed and modeled. A fabrication process utilizing two sided anisotropic etching of {110} silicon wafers is developed. The process utilizes standard microelectronic fabrication equipment to batch fabricate the isolation systems. The fabricated systems are only 1 cm by 1 cm by 1 mm. Several oscillators are fabricated using commercially fabricated STW resonators mounted on the isolation systems. The resonators are driven by their standard oscillator circuit. Incorporating the isolation system into the oscillator does not result in an appreciable increase the size or the weight of the oscillator. Testing of the oscillators shows that the isolators successfully function as passive vibration isolation systems

Towards micro-assembly of hybrid MOEMS components on reconfigurable silicon free-space micro-optical bench.

International audienceThe 3D integration of hybrid chips is a viable approach for the micro-optical technologies to reduce the costs of assembly and packaging. In this paper a technology platform for the hybrid integration of MOEMS components on a reconfigurable free-space silicon micro-optical bench is presented. In this approach a desired optical component (e.g. micromirror, microlens) is integrated with removable and adjustable silicon holder which can be manipulated, aligned and fixed in the precisely etched rail of the silicon baseplate by use of robotic micro-assembly station. An active-based gripping system allows modification of the holder position on the baseplate with nanometre precision. The fabrication processes of the micromachined parts of the micro-optical bench, based on bulk micromachining of standard silicon wafer and SOI wafer, are described. The successful assembly of the holders, equipped with micromirror and refractive glass ball microlens, on the baseplate rail is demonstrated

High performance readout circuits and devices for Lorentz force resonant CMOS-MEMS magnetic sensors

In the last decades, sensing capabilities of martphones have greatly improved since the early mobile phones of the 90’s. Moreover, wearables and the automotive industry require increasing electronics and sensing sophistication. In such echnological advance, Micro Electro Mechanical Systems (MEMS) have played an important role as accelerometers and gyroscopes were the first sensors based on MEMS technology massively introduced in the market. In contrast, it still does not exist a commercial MEMS-based compass, even though Lorentz force MEMS magnetometers were first proposed in the late 90’s. Currently, Lorentz force MEMS magnetometers have been under the spotlight as they can offer an integrated solution to nowadays sensing power. As a consequence, great advances have been achieved, but various bottlenecks limit the introduction of Lorentz force MEMS compasses in the market. First, current MEMS magnetometers require high current consumption and high biasing voltages to achieve good sensitivities. Moreover, even though devices with excellent performance and sophistication are found in the literature, there is still a lack of research on the readout electronic circuits, specially in the digital signal processing, and closed loop control. Second, most research outcomes rely on custom MEMS fabrication rocesses to manufacture the devices. This is the same approach followed in current commercial MEMS, but it requires different fabrication processes for the electronics and the MEMS. As a consequence, manufacturing cost is high and sensor performance is affected by the MEMS-electronics interface parasitics. This dissertation presents potential solutions to these issues in order to pave the road to the commercialization of Lorentz force MEMS compasses. First, a complete closed loop, digitally controlled readout system is proposed. The readout circuitry, implemented with off-the-shelf commercial components, and the digital control, on an FPGA, are proposed as a proof of concept of the feasibility, and potential benefits, of such architecture. The proposed system has a measured noise of 550 nT / vHz while the MEMS is biased with 300 µA rms and V = 1 V . Second, various CMOS-MEMS magnetometers have been designed using the BEOL part of the TSMC and SMIC 180 nm standard CMOS processes, and wet and vapor etched. The devices measurement and characterisation is used to analyse the benefits and drawbacks of each design as well as releasing process. Doing so, a high volume manufacturing viability can be performed. Yield values as high as 86% have been obtained for one device manufactured in a SMIC 180 nm full wafer run, having a sensitivity of 2.82 fA/µT · mA and quality factor Q = 7.29 at ambient pressure. While a device manufactured in TSMC 180 nm has Q = 634.5 and a sensitivity of 20.26 fA/µT ·mA at 1 mbar and V = 1 V. Finally, an integrated circuit has been designed that contains all the critical blocks to perform the MEMS signal readout. The MEMS and the electronics have been manufactured using the same die area and standard TSMC 180 nm process in order to reduce parasitics and improve noise and current consumption. Simulations show that a resolution of 8.23 µT /mA for V = 1 V and BW = 10 Hz can be achieved with the designed device.En les últimes dècades, tenint en compte els primers telèfons mòbils dels anys 90, les capacitats de sensat dels telèfons intel·ligents han millorat notablement. A més, la indústria automobilística i de wearables necessiten cada cop més sofisticació en el sensat. Els Micro Electro Mechanical Systems (MEMS) han tingut un paper molt important en aquest avenç tecnològic, ja que acceleròmetres i giroscopis varen ser els primers sensors basats en la tecnologia MEMS en ser introduïts massivament al mercat. En canvi, encara no existeix en la indústria una brúixola electrònica basada en la tecnologia MEMS, tot i que els magnetòmetres MEMS varen ser proposats per primera vegada a finals dels anys 90. Actualment, els magnetòmetres MEMS basats en la força de Lorentz són el centre d'atenció donat que poden oferir una solució integrada a les capacitats de sensat actuals. Com a conseqüència, s'han aconseguit grans avenços encara que existeixen diversos colls d'ampolla que encara limiten la introducció al mercat de brúixoles electròniques MEMS basades en la força de Lorentz. Per una banda, els agnetòmetres MEMS actuals necessiten un consum de corrent i un voltatge de polarització elevats per aconseguir una bona sensibilitat. A més, tot i que a la literatura hi podem trobar dispositius amb rendiments i sofisticació excel·lents, encara existeix una manca de recerca en el circuit de condicionament, especialment de processat digital i control del llaç. Per altra banda, moltes publicacions depenen de processos de fabricació de MEMS fets a mida per fabricar els dispositius. Aquesta és la mateixa aproximació que s'utilitza actualment en la indústria dels MEMS, però té l'inconvenient que requereix processos de fabricació diferents pels MEMS i l’electrònica. Per tant, el cost de fabricació és alt i el rendiment del sensor queda afectat pels paràsits en la interfície entre els MEMS i l'electrònica. Aquesta tesi presenta solucions potencials a aquests problemes amb l'objectiu d'aplanar el camí a la comercialització de brúixoles electròniques MEMS basades en la força de Lorentz. En primer lloc, es proposa un circuit de condicionament complet en llaç tancat controlat digitalment. Aquest s'ha implementat amb components comercials, mentre que el control digital del llaç s'ha implementat en una FPGA, tot com una prova de concepte de la viabilitat i beneficis potencials que representa l'arquitectura proposada. El sistema presenta un soroll de 550 nT / vHz quan el MEMS està polaritzat amb 300 µArms i V = 1 V . En segon lloc, s'han dissenyat varis magnetòmetres CMOS-MEMS utilitzant la part BEOL dels processos CMOS estàndard de TSMC i SMIC 180 nm, que després s'han alliberat amb líquid i gas. La mesura i caracterització dels dispositius s’ha utilitzat per analitzar els beneficis i inconvenients de cada disseny i procés d’alliberament. D'aquesta manera, s'ha pogut realitzar un anàlisi de la viabilitat de la seva fabricació en massa. S'han obtingut valors de yield de fins al 86% per un dispositiu fabricat amb SMIC 180 nm en una oblia completa, amb una sensibilitat de 2.82 fA/µT · mA i un factor de qualitat Q = 7.29 a pressió ambient. Per altra banda, el dispositiu fabricat amb TSMC 180 nm presenta una Q = 634.5 i una sensibilitat de 20.26 fA/µT · mA a 1 mbar amb V = 1 V. Finalment, s'ha dissenyat un circuit integrat que conté tots els blocs per a realitzar el condicionament de senyal del MEMS. El MEMS i l'electrònica s'han fabricat en el mateix dau amb el procés estàndard de TSMC 180 nm per tal de reduir paràsits i millorar el soroll i el consum de corrent. Les simulacions mostren una resolució de 8.23 µT /mA amb V = 1 V i BW = 10 Hz pel dispositiu dissenyat

Platform-based design, test and fast verification flow for mixed-signal systems on chip

This research is providing methodologies to enhance the design phase from architectural space exploration and system study to verification of the whole mixed-signal system. At the beginning of the work, some innovative digital IPs have been designed to develop efficient signal conditioning for sensor systems on-chip that has been included in commercial products. After this phase, the main focus has been addressed to the creation of a re-usable and versatile test of the device after the tape-out which is close to become one of the major cost factor for ICs companies, strongly linking it to model’s test-benches to avoid re-design phases and multi-environment scenarios, producing a very effective approach to a single, fast and reliable multi-level verification environment. All these works generated different publications in scientific literature. The compound scenario concerning the development of sensor systems is presented in Chapter 1, together with an overview of the related market with a particular focus on the latest MEMS and MOEMS technology devices, and their applications in various segments. Chapter 2 introduces the state of the art for sensor interfaces: the generic sensor interface concept (based on sharing the same electronics among similar applications achieving cost saving at the expense of area and performance loss) versus the Platform Based Design methodology, which overcomes the drawbacks of the classic solution by keeping the generality at the highest design layers and customizing the platform for a target sensor achieving optimized performances. An evolution of Platform Based Design achieved by implementation into silicon of the ISIF (Intelligent Sensor InterFace) platform is therefore presented. ISIF is a highly configurable mixed-signal chip which allows designers to perform an effective design space exploration and to evaluate directly on silicon the system performances avoiding the critical and time consuming analysis required by standard platform based approach. In chapter 3 we describe the design of a smart sensor interface for conditioning next generation MOEMS. The adoption of a new, high performance and high integrated technology allow us to integrate not only a versatile platform but also a powerful ARM processor and various IPs providing the possibility to use the platform not only as a conditioning platform but also as a processing unit for the application. In this chapter a description of the various blocks is given, with a particular emphasis on the IP developed in order to grant the highest grade of flexibility with the minimum area occupation. The architectural space evaluation and the application prototyping with ISIF has enabled an effective, rapid and low risk development of a new high performance platform achieving a flexible sensor system for MEMS and MOEMS monitoring and conditioning. The platform has been design to cover very challenging test-benches, like a laser-based projector device. In this way the platform will not only be able to effectively handle the sensor but also all the system that can be built around it, reducing the needed for further electronics and resulting in an efficient test bench for the algorithm developed to drive the system. The high costs in ASIC development are mainly related to re-design phases because of missing complete top-level tests. Analog and digital parts design flows are separately verified. Starting from these considerations, in the last chapter a complete test environment for complex mixed-signal chips is presented. A semi-automatic VHDL-AMS flow to provide totally matching top-level is described and then, an evolution for fast self-checking test development for both model and real chip verification is proposed. By the introduction of a Python interface, the designer can easily perform interactive tests to cover all the features verification (e.g. calibration and trimming) into the design phase and check them all with the same environment on the real chip after the tape-out. This strategy has been tested on a consumer 3D-gyro for consumer application, in collaboration with SensorDynamics AG