National MEMS Technology Roadmap - Markets, Applications and Devices

MEMS teknologiaa on jo pitkään käytetty lukuisien eri laitteiden valmistamiseen. Osa näistä laitteista on ollut markkinoilla jo useita vuosia, kun taas osa on vasta kehitysvaiheessa. Jotta tutkimus ja kehitystyötä osattaisiin jatkossa kohdistaa oikeille painopistealueille, on tärkeää tietää mihin suuntaan kehitys on menossa. Tämä työ on osa kansallista MEMS teknologioiden tiekartta -projektia ja sen tavoitteena oli selvittää MEMS laitteiden kehityksen suuntaa. Työ toteutettiin laajana kirjallisuustutkimuksena. Lisäksi tulosten tueksi haastateltiin asiantuntijoita Suomen MEMS teollisuudesta. Työssä tarkasteltiin lukuisia jo markkinoilta löytyviä ja vasta kehitteillä olevia MEMS laitteita ja analysoitiin niitä sekä teknisestä että kaupallisesta näkökulmasta. Tutkimuksen perusteella kävi ilmi, että MEMS markkinat ovat pitkään muodostuneet vakiintuneista laitteista kuten mustesuihkupäistä, kiihtyvyysantureista, paineantureista sekä RF suotimista. Lisäksi mikrofonit, gyroskoopit ja optiset laitteet ovat olleet kaupallisesti saatavilla jo pitkään. Markkinat ovat hiljattain alkaneet tehdä tilaa myös uusille MEMS laitteille, joita tulee ulos nopeaa vauhtia. Viimeisimpänä markkinoille tulleita laitteita ovat erilaiset mikrofluidistiikka laitteet, mikrobolometrit sekä yhdistelmäanturit. Pian kaupallisesti saatavia laitteita ovat magnetometrit, automaattitarkennuslaitteet sekä MEMS oskillaattorit. Näiden laitteiden lisäksi kehitteillä on monia uusia MEMS laitteita, jotka saattavat tarjota merkittäviä mahdollisuuksia tulevaisuudessa. Kehitteillä olevia laitteita ovat erilaiset lääketieteelliset laitteet, atomikellot, mikrojäähdyttimet, mikrokaiuttimet, energiantuottolaitteet sekä RFID-laitteet. Kaikki kehitteillä olevista laitteista eivät välttämättä tule menestymään kaupallisesti, mutta jatkuva tutkimustyö osoittaa, että monilla MEMS laitteilla on potentiaalia useissa eri sovelluksissa. Markkinanäkökulmasta tarkasteltuna suurin potentiaali piilee kuluttajaelektroniikka markkinoilla. Muita tulevaisuuden kannalta potentiaalisia markkinoita ovat lääketieteelliset ja teollisuusmarkkinat. Tutkimus osoitti että MEMS laitteiden tutkimukseen ja kehitykseen liittyy monia potentiaalisia painopistealueita tulevaisuudessa. Käyttömahdollisuuksien parantamiseksi monet jo vakiintuneet laitteet kaipaavat vielä parannuksia. Toisaalta, jo olemassa olevia laitteita voidaan hyödyntää uusissa sovelluksissa. Lisäksi monet uusista ja kehitteillä olevista MEMS laitteista vaativat vielä kehitystyötä.MEMS technology has long been applied to the fabrication of various devices from which some have already been in use for several years, whereas others are still under development. In order to find future focus areas in research and development activities in the industry, it is important to know where the development is going. This thesis was conducted as a part of National MEMS technology roadmap, and it aimed for determining the evolution of MEMS devices. The work was conducted as an extensive literature review. In addition, experts from the Finnish MEMS industry were interviewed in order obtain a broader insight to the results. In this thesis various existing and emerging MEMS devices were reviewed and analyzed from technological and commercial perspectives. The study showed that the MEMS market has long been composed of established devices, such as inkjet print-heads, pressure sensors, accelerometers and RF filters. Also gyroscopes, microphones and optical MEMS devices have already been on the market for a long time. Lately, many new devices have started to find their place in the markets. The most recently introduced commercial devices include microfluidic devices, micro bolometers, and combo sensors. There are also a few devices including magnetometers, MEMS oscillators, and auto-focus devices that are currently crossing the gap from R&D to commercialization. In addition to the already available devices, many new MEMS devices are under development, and might offer significant opportunities in the future. These emerging devices include various bioMEMS devices, atomic clocks, micro-coolers, micro speakers, power MEMS devices, and RFID devices. All of the emerging devices might not find commercial success, but the constant stream shows, that there are numerous applications, where MEMS devices could be applied in. From a market point of view, the greatest potential in the future lies in consumer electronics market. Other highly potential markets include medical and industrial markets. The results of the thesis indicate that there are many potential focus areas in the future related to MEMS devices, including improvements of the existing devices in order to gain better utilization, application of the existing devices in new areas, and development work among the emerging devices

Ultra-Low Power Circuit Design for Cubic-Millimeter Wireless Sensor Platform.

Modern daily life is surrounded by smaller and smaller computing devices. As Bell’s Law predicts, the research community is now looking at tiny computing platforms and mm3-scale sensor systems are drawing an increasing amount of attention since they can create a whole new computing environment. Designing mm3-scale sensor nodes raises various circuit and system level challenges and we have addressed and proposed novel solutions for many of these challenges to create the first complete 1.0mm3 sensor system including a commercial microprocessor. We demonstrate a 1.0mm3 form factor sensor whose modular die-stacked structure allows maximum volume utilization. Low power I2C communication enables inter-layer serial communication without losing compatibility to standard I2C communication protocol. A dual microprocessor enables concurrent computation for the sensor node control and measurement data processing. A multi-modal power management unit allowed energy harvesting from various harvesting sources. An optical communication scheme is provided for initial programming, synchronization and re-programming after recovery from battery discharge. Standby power reduction techniques are investigated and a super cut-off power gating scheme with an ultra-low power charge pump reduces the standby power of logic circuits by 2-19× and memory by 30%. Different approaches for designing low-power memory for mm3-scale sensor nodes are also presented in this work. A dual threshold voltage gain cell eDRAM design achieves the lowest eDRAM retention power and a 7T SRAM design based on hetero-junction tunneling transistors reduces the standby power of SRAM by 9-19× with only 15% area overhead. We have paid special attention to the timer for the mm3-scale sensor systems and propose a multi-stage gate-leakage-based timer to limit the standard deviation of the error in hourly measurement to 196ms and a temperature compensation scheme reduces temperature dependency to 31ppm/°C. These techniques for designing ultra-low power circuits for a mm3-scale sensor enable implementation of a 1.0mm3 sensor node, which can be used as a skeleton for future micro-sensor systems in variety of applications. These microsystems imply the continuation of the Bell’s Law, which also predicts the massive deployment of mm3-scale computing systems and emergence of even smaller and more powerful computing systems in the near future.Ph.D.Electrical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/91438/1/sori_1.pd

Self-powered Time-Keeping and Time-of-Occurrence Sensing

Self-powered and passive Internet-of-Things (IoT) devices (e.g. RFID tags, financial assets, wireless sensors and surface-mount devices) have been widely deployed in our everyday and industrial applications. While diverse functionalities have been implemented in passive systems, the lack of a reference clock limits the design space of such devices used for applications such as time-stamping sensing, recording and dynamic authentication. Self-powered time-keeping in passive systems has been challenging because they do not have access to continuous power sources. While energy transducers can harvest power from ambient environment, the intermittent power cannot support continuous operation for reference clocks. The thesis of this dissertation is to implement self-powered time-keeping devices on standard CMOS processes. In this dissertation, a novel device that combines the physics of quantum tunneling and floating-gate (FG) structures is proposed for self-powered time-keeping in CMOS process. The proposed device is based on thermally assisted Fowler-Nordheim (FN) tunneling process across high-quality oxide layer to discharge the floating-gate node, therefore resulting in a time-dependent FG potential. The device was fully characterized in this dissertation, and it does not require external powering during runtime, making it feasible for passive devices and systems. Dynamic signature based on the synchronization and desynchronization behavior of the FN timer is proposed for authentication of IoT devices. The self-compensating physics ensure that when distributed timers are subjected to identical environment variances that are common-mode noise, they can maintain synchronization with respect to each other. On the contrary, different environment conditions will desynchronize the timers creating unique signatures. The signatures could be used to differentiate between products that belong to different supply-chains or products that were subjected to malicious tampering. SecureID type dynamic authentication protocols based on the signature generated by the FN timers are proposed and they are proven to be robust to most attacks. The protocols are further analyzed to be lightweight enough for passive devices whose computational sources are limited. The device could also be applied for self-powered sensing of time-of-occurrence. The prototype was verified by integrating the device with a self-powered mechanical sensor to sense and record time-of-occurrence of mechanical events. The system-on-chip design uses the timer output to modulate a linear injector to stamp the time information into the sensing results. Time-of-occurrence can be reconstructed by training the mathematical model and then applying that to the test data. The design was verified to have a high reconstruction accuracy

Interface Circuits for Microsensor Integrated Systems

ca. 200 words; this text will present the book in all promotional forms (e.g. flyers). Please describe the book in straightforward and consumer-friendly terms. [Recent advances in sensing technologies, especially those for Microsensor Integrated Systems, have led to several new commercial applications. Among these, low voltage and low power circuit architectures have gained growing attention, being suitable for portable long battery life devices. The aim is to improve the performances of actual interface circuits and systems, both in terms of voltage mode and current mode, in order to overcome the potential problems due to technology scaling and different technology integrations. Related problems, especially those concerning parasitics, lead to a severe interface design attention, especially concerning the analog front-end and novel and smart architecture must be explored and tested, both at simulation and prototype level. Moreover, the growing demand for autonomous systems gets even harder the interface design due to the need of energy-aware cost-effective circuit interfaces integrating, where possible, energy harvesting solutions. The objective of this Special Issue is to explore the potential solutions to overcome actual limitations in sensor interface circuits and systems, especially those for low voltage and low power Microsensor Integrated Systems. The present Special Issue aims to present and highlight the advances and the latest novel and emergent results on this topic, showing best practices, implementations and applications. The Guest Editors invite to submit original research contributions dealing with sensor interfacing related to this specific topic. Additionally, application oriented and review papers are encouraged.

Silicon carbide technology for extreme environments

PhD ThesisWith mankind’s ever increasing curiosity to explore the unknown, including a variety of hostile environments where we cannot tread, there exists a need for machines to do work on our behalf. For applications in the most extreme environments and applications silicon based electronics cannot function, and there is a requirement for circuits and sensors to be built from wide band gap materials capable of operation in these domains. This work addresses the initial development of silicon carbide circuits to monitor conditions and transmit information from such hostile environments. The characterisation, simulation and implementation of silicon carbide based circuits utilising proprietary high temperature passives is explored. Silicon carbide is a wide band gap semiconductor material with highly suitable properties for high-power, high frequency and high temperature applications. The bandgap varies depending on polytype, but the most commonly used polytype 4H, has a value of 3.265 eV at room temperature, which reduces as the thermal ionization of electrons from the valence band to the conduction band increases, allowing operation in ambient up to 600°C. Whilst silicon carbide allows for the growth of a native oxide, the quality has limitations and therefore junction field effect transistors (JFETs) have been utilised as the switch in this work. The characteristics of JFET devices are similar to those of early thermionic valve technology and their use in circuits is well known. In conjunction with JFETs, Schottky barrier diodes (SBDs) have been used as both varactors and rectifiers. Simulation models for high temperature components have been created through their characterisation of their electrical parameters at elevated temperatures. The JFETs were characterised at temperatures up to 573K, and values for TO V , β , λ , IS , RS and junction capacitances were extracted and then used to mathematically describe the operation of circuits using SPICE. The transconductance of SiC JFETs at high temperatures has been shown to decrease quadratically indicating a strong dependence upon carrier mobility in the channel. The channel resistance also decreased quadratically as a direct result of both electric field and temperature enhanced trap emission. The JFETs were tested to be operational up to 775K, where they failed due to delamination of an external passivation layer. ii Schottky diodes were characterised up to 573K, across the temperature range and values for ideality factor, capacitance, series resistance and forward voltage drop were extracted to mathematically model the devices. The series resistance of a SiC SBD exhibited a quadratic relationship with temperature indicating that it is dominated by optical phonon scattering of charge carriers. The observed deviation from a temperature independent ideality factor is due to the recombination of carriers in the depletion region affected by both traps and the formation of an interfacial layer at the SiC/metal interface. To compliment the silicon carbide active devices utilised in this work, high temperature passive devices and packaging/circuit boards were developed. Both HfO2 and AlN materials were investigated for use as potential high temperature capacitor dielectrics in metal-insulator-metal (MIM) capacitor structures. The different thicknesses of HfO2 (60nm and 90nm) and 300nm for AlN and the relevance to fabrication techniques are examined and their effective capacitor behaviour at high temperature explored. The HfO2 based capacitor structures exhibited high levels of leakage current at temperatures above 100°C. Along with elevated leakage when subjected to higher electric fields. This current leakage is due to the thin dielectric and high defect density and essentially turns the capacitors into high value resistors in the order of MΩ. This renders the devices unsuitable as capacitors in hostile environments at the scales tested. To address this issue AlN capacitors with a greater dielectric film thickness were fabricated with reduced leakage currents in comparison even at an electric field of 50MV/cm at 600K. The work demonstrated the world’s first high temperature wireless sensor node powered using energy harvesting technology, capable of operation at 573K. The module demonstrated the world’s first amplitude modulation (AM) and frequency modulation (FM) communication techniques at high temperature. It also demonstrated a novel high temperature self oscillating boost converter cable of boosting voltages from a thermoelectric generator also operating at this temperature. The AM oscillator operated at a maximum temperature of 553K and at a frequency of 19.4MHz with a signal amplitude 65dB above background noise. Realised from JFETs and HfO2 capacitors, modulation of the output signal was achieved by varying the load resistance by use of a second SiC JFET. By applying a negative signal voltage of between -2.5 and -3V, a 50% reduction in the signal amplitude and therefore Amplitude Modulation was achieved by modulating the power within the oscillator through the use of this secondary JFET. Temperature drift in the characteristics were also observed, iii with a decrease in oscillation frequency of almost 200 kHz when the temperature changed from 300K to 573K. This decrease is due to the increase in capacitance density of the HfO2 MIM capacitors and increasing junction capacitances of the JFET used as the amplifier within the oscillator circuit. Direct frequency modulation of a SiC Voltage Controlled Oscillator was demonstrated at a temperature of 573K with a oscillation frequency of 17MHz. Realised from an SiC JFET, AlN capacitors and a SiC SBD used as a varactor. It was possible to vary the frequency of oscillations by 100 kHz with an input signal no greater than 1.5V being applied to the SiC SBD. The effects of temperature drift were more dramatic in comparison to the AM circuit at 400 kHz over the entire temperature range, a result of the properties of the AlN film which causes the capacitors to increase in capacitance density by 10%. A novel self oscillating boost converter was commissioned using a counter wound transformer on high temperature ferrite, a SiC JFET and a SiC SBD. Based upon the operation of a free running blocking oscillator, oscillatory behaviour is a result of the electric and magnetic variations in the winding of the transformer and the amplification characteristics of a JFET. It demonstrated the ability to boost an input voltage of 1.3 volts to 3.9 volts at 573K and exhibited an efficiency of 30% at room temperature. The frequency of operation was highly dependent upon the input voltage due to the increased current flow through the primary coil portion of the transformer and the ambient temperature causing an increase in permeability of the ferrite, thus altering the inductance of both primary and secondary windings. However due its simplicity and its ability to boost the input voltage by 250% meant it was capable of powering the transmitters and in conjunction with a Themoelectric Generator so formed the basis for a self powered high temperature silicon carbide sensor node. The demonstration of these high temperature circuits provide the initial stages of being able to produce a high temperature wireless sensor node capable of operation in hostile environments. Utilising the self oscillating boost converter and a high temperature Thermoelectric Generator these prototype circuits were showed the ability to harvest energy from the high temperature ambient and power the silicon carbide circuitry. Along with appropriate sensor technology it demonstrated the feasibility of being able to monitor and transmit information from hazardous locations which is currently unachievable

Millimeter-Scale and Energy-Efficient RF Wireless System

This dissertation focuses on energy-efficient RF wireless system with millimeter-scale dimension, expanding the potential use cases of millimeter-scale computing devices. It is challenging to develop RF wireless system in such constrained space. First, millimeter-sized antennae are electrically-small, resulting in low antenna efficiency. Second, their energy source is very limited due to the small battery and/or energy harvester. Third, it is required to eliminate most or all off-chip devices to further reduce system dimension. In this dissertation, these challenges are explored and analyzed, and new methods are proposed to solve them. Three prototype RF systems were implemented for demonstration and verification. The first prototype is a 10 cubic-mm inductive-coupled radio system that can be implanted through a syringe, aimed at healthcare applications with constrained space. The second prototype is a 3x3x3 mm far-field 915MHz radio system with 20-meter NLOS range in indoor environment. The third prototype is a low-power BLE transmitter using 3.5x3.5 mm planar loop antenna, enabling millimeter-scale sensors to connect with ubiquitous IoT BLE-compliant devices. The work presented in this dissertation improves use cases of millimeter-scale computers by presenting new methods for improving energy efficiency of wireless radio system with extremely small dimensions. The impact is significant in the age of IoT when everything will be connected in daily life.PHDElectrical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttps://deepblue.lib.umich.edu/bitstream/2027.42/147686/1/yaoshi_1.pd

Energy autonomous systems : future trends in devices, technology, and systems

The rapid evolution of electronic devices since the beginning of the nanoelectronics era has brought about exceptional computational power in an ever shrinking system footprint. This has enabled among others the wealth of nomadic battery powered wireless systems (smart phones, mp3 players, GPS, …) that society currently enjoys. Emerging integration technologies enabling even smaller volumes and the associated increased functional density may bring about a new revolution in systems targeting wearable healthcare, wellness, lifestyle and industrial monitoring applications