Showing papers by "Michael Kraft published in 2014"

Fabrication and operation of a two-dimensional ion-trap lattice on a high-voltage microchip.

Abstract: Microfabricated ion traps are a major advancement towards scalable quantum computing with trapped ions. The development of more versatile ion-trap designs, in which tailored arrays of ions are positioned in two dimensions above a microfabricated surface, will lead to applications in fields as varied as quantum simulation, metrology and atom–ion interactions. Current surface ion traps often have low trap depths and high heating rates, because of the size of the voltages that can be applied to them, limiting the fidelity of quantum gates. Here we report on a fabrication process that allows for the application of very high voltages to microfabricated devices in general and use this advance to fabricate a two-dimensional ion-trap lattice on a microchip. Our microfabricated architecture allows for reliable trapping of two-dimensional ion lattices, long ion lifetimes, rudimentary shuttling between lattice sites and the ability to deterministically introduce defects into the ion lattice.

A rotary comb-actuated microgripper with a large displacement range

Abstract: This paper reports a novel design for electrostatic microgrippers. The new structure utilizes rotary comb actuators to solve the pull-in problem of microgrippers during large displacement manipulation and therefore avoids the widely used conversion systems which necessitate a high driving voltage. The gripper is fabricated using a SOI process with a 60 μm structural layer. Test results show the gripper obtained a displacement of 94 μm with an applied voltage of 100 V. An animal hair is gripped to demonstrate the applicability of the gripper for micro object manipulations.

Design and Implementation of an Optimized Double Closed-Loop Control System for MEMS Vibratory Gyroscope

Abstract: This paper describes the development and experimental evaluation of a microelectromechanical system vibratory gyroscope using an optimized double closed-loop control strategy. An automatic gain control self-oscillation interface is used to resonate the gyroscope in the drive mode; the sense mode is controlled by a sixth-order continuous-time and force-feedback band-pass sigma-delta modulator. The parameters of both control loops are optimized by a genetic algorithm (GA). System level simulations show that the settling time of the drive mode self-oscillation is 125 ms, the root mean square displacement of the proof mass is in the sense mode, and the signal-to-noise ratio is 90 dB in a bandwidth of 64 Hz with a 200 °/s angular rate input signal. The system is implemented using symmetrical and fully decoupled silicon on insulator gyroscope operating at atmospheric with the circuit implemented on printed circuit board. The measured power spectral density of the output bitstream shows an obvious band-pass noise shaping and a deep notch at the gyroscope resonant frequency. The measured noise floor is approximately -120 dBV/Hz1/2. In the drive mode, the relative drift of the resonant frequency and amplitude is 3.2 and 10.7 ppm for 1 h measurements, respectively. The settling time, scale factor, zero bias stability, and bandwidth of the gyroscope controlled by the optimized control system are 200 ms, 22.5 mV/°/s, 34 °/h, and 110 Hz, respectively. This is compared with a non-optimized system for which the corresponding values are 300 ms, 17.3 mV/°/s, 58 °/h, and 98 Hz; hence, by GA optimization a considerable performance improvement is achieved.

Low noise vacuum MEMS closed-loop accelerometer using sixth-order multi-feedback loops and local resonator sigma delta modulator

Abstract: This paper reports on the design, implementation of a novel sixth-order sigma-delta modulator (ΣΔM) MEMS closed-loop accelerometer with extended bandwidth in a vacuum environment (~0.5Torr), which can coexist on a single die (or package) with other sensors requiring vacuum packaging. The fully differential accelerometer sensing element with a large proof mass (4×7mm2) was designed and fabricated on a Silicon-on-Insulator (SOI) wafer with 50μm-thick structural layer. Four electronic integrators were cascaded with the sensing element for high-order noise shaping ability. The local feedback paths created a local resonator producing a notch to further suppress the total in-band quantization noise. Measurement results show the overall noise floor achieved was -120dBg/√Hz, which is equivalent to a noise acceleration value of 1.2μg/√Hz in a 500Hz bandwidth; the scale factor was 950mV/g for input accelerations up to ±6g.

Solar thermoelectric generators fabricated on a silicon-on-insulator substrate

Abstract: Solar thermal power generation is an attractive electricity generation technology as it is environment-friendly, has the potential for increased efficiency, and has high reliability. The design, modelling, and evaluation of solar thermoelectric generators (STEGs) fabricated on a silicon-on-insulator substrate are presented in this paper. Solar concentration is achieved by using a focusing lens to concentrate solar input onto the membrane of the STEG. A thermal model is developed based on energy balance and heat transfer equations using lumped thermal conductances. This thermal model is shown to be in good agreement with actual measurement results. For a 1 W laser input with a spot size of 1 mm, a maximum open-circuit voltage of 3.06 V is obtained, which translates to a temperature difference of 226 °C across the thermoelements and delivers 25 µW of output power under matched load conditions. Based on solar simulator measurements, a maximum TEG voltage of 803 mV was achieved by using a 50.8 mm diameter plano-convex lens to focus solar input to a TEG with a length of 1000 µm, width of 15 µm, membrane diameter of 3 mm, and 114 thermocouples. This translates to a temperature difference of 18 °C across the thermoelements and an output power under matched load conditions of 431 nW.This paper demonstrates that by utilizing a solar concentrator to focus solar radiation onto the hot junction of a TEG, the temperature difference across the device is increased; subsequently improving the TEG's efficiency. By using materials that are compatible with standard CMOS and MEMS processes, integration of solar-driven TEGs with on-chip electronics is seen to be a viable way of solar energy harvesting where the resulting microscale system is envisioned to have promising applications in on-board power sources, sensor networks, and autonomous microsystems.

Non-invasive synchronized spatially high-resolution wireless body area network

Abstract: Wireless body sensor networks consisting of EEG, ECG, EMG and acceleration sensors provide assistance to the researchers in cognitive physiology and clinical research as well as in neurophysiology The data fusion of the electrical activities of muscle structures, eg facial muscles, heart and brain combined with the movement data of patients helps to detect nocturnal epileptic seizure in home care application A mobile, flexible, densely configurable distributed body area network featuring wireless data transmission and a wired time synchronization technique was designed and realized in this work Signal conditioning of each of sensor systems was realized depending on their signal strength and frequency bandwidth Moreover, synchronization between each of the nodes was achieved with the help of wired USART (universal synchronous/asynchronous receiver/transmitter) All measurement units follow the same synchronization protocol, which is controlled by a master unit The ExG-system can sample bio-potentials from 125 Hz up to 1000 Hz and it exhibits 1445 μν peak-to-peak system noise between 01 Hz and 500 Hz and can send data with incorporated Wi-Fi module in it to a basis station at a maximum data speed of 145 Mbps A 3–4 cm spatial resolution can be achieved for high-dense EEG during a complete 256 channel deployment

Design, Modeling, Fabrication, and Evaluation of Thermoelectric Generators with Hot-Wire Chemical Vapor Deposited Polysilicon as Thermoelement Material

Abstract: This paper presents the design, modeling, fabrication, and evaluation of thermoelectric generators (TEGs) with p-type polysilicon deposited by hot-wire chemical vapor deposition (HWCVD) as thermoelement material. A thermal model is developed based on energy balance and heat transfer equations using lumped thermal conductances. Several test structures were fabricated to allow characterization of the boron-doped polysilicon material deposited by HWCVD. The film was found to be electrically active without any post-deposition annealing. Based on the tests performed on the test structures, it is determined that the Seebeck coefficient, thermal conductivity, and electrical resistivity of the HWCVD polysilicon are 113 μV/K, 126 W/mK, and 3.58 × 10−5 Ω m, respectively. Results from laser tests performed on the fabricated TEG are in good agreement with the thermal model. The temperature values derived from the thermal model are within 2.8% of the measured temperature values. For a 1-W laser input, an open-circuit voltage and output power of 247 mV and 347 nW, respectively, were generated. This translates to a temperature difference of 63°C across the thermoelements. This paper demonstrates that HWCVD, which is a cost-effective way of producing solar cells, can also be applied in the production of TEGs. By establishing that HWCVD polysilicon can be an effective thermoelectric material, further work on developing photovoltaic-thermoelectric (PV-TE) hybrid microsystems that are cost-effective and better performing can be explored.

Encapsulation of implantable integrated MEMS pressure sensors using polyimide epoxy composite and atomic layer deposition

Abstract: . Implantable MEMS sensors are an enabling technology for diagnostic analysis and therapy in medicine. The encapsulation of such miniaturized implants remains a largely unsolved problem. Medically approved encapsulation materials include titanium or ceramics; however, these result in bulky and thick-walled encapsulations which are not suitable for MEMS sensors. In particular, for MEMS pressure sensors the chip surface comprising the pressure membranes must be free of rigid encapsulation material and in direct contact with tissue or body fluids. This work describes a new kind of encapsulation approach for a capacitive pressure sensor module consisting of two integrated circuits. The micromechanical membrane of the pressure sensor may be covered only by very thin layers, to ensure high pressure sensitivity. A suitable passivation method for the high topography of the pressure sensor is atomic layer deposition (ALD) of aluminium oxide (Al2O3) and tantalum pentoxide (Ta2O5). It provides a hermetic passivation with a high conformity. Prior to ALD coating, a high-temperature resistant polyimide–epoxy composite was evaluated as a die attach material and sealing compound for bond wires and the chip surface. This can sustain the ALD deposition temperature of 275 °C for several hours without any measurable decomposition. Tests indicated that the ALD can be deposited on top of the polyimide–epoxy composite covering the entire sensor module. The encapsulated pressure sensor module was calibrated and tested in an environmental chamber at accelerated aging conditions. An accelerated life test at 60 °C indicated a maximum drift of 5% full scale after 1482 h. From accelerated life time testing at 120 °C a maximum stable life time of 3.3 years could be extrapolated.

Wireless time synchronization of a collaborative brain-computer-interface using bluetooth low energy

Abstract: A wireless EEG-system with high channel density (up to 256) was developed for bio-potential data recording. In order to use this system for a collaborative brain-computer-interface (BCI) multiple EEG sub-systems with a common visually and auditory evoked potential (VEP/AEP) stimulator, a video camera and a PC, all connected to a WLAN, are required. Since each of the components has its own software clock typically based on a quartz crystal, a difference in skew and offset between all system components is induced after a few seconds from their cold start; this is due to the quartz instability of ±50 ppm. To evaluate evoked potentials of different test subjects synchronous in time in a group experiment scenario, it is necessary to implement a common time reference among the entire system. To achieve time synchronization without modifying the existing hardware/software a novel synchronization add-on, and a synchronization center based on Bluetooth were implemented and experimentally evaluated.

Two-degree of freedom capacitive MEMS velocity sensor with two coupled electrically isolated mass-spring-damper systems

Abstract: This paper presents initial experimental results obtained with a novel two degree of freedom (2-DOF) capacitive MEMS sensor intended for vibration control applications. The sensor comprises a principal spring-mass system mechanically in series with a secondary spring-mass system for the implementation of an internal feedback loop. The control loop produces a sky-hook damping force on the principal system, so that the output of the sensor becomes proportional to the base velocity rather than the base acceleration. The design proposed in this work enables direct capacitive displacement sensing of the secondary proof mass with respect to the principal sensor. The sensor closed loop response function is characterized by a low frequency (400-1000 Hz) flat spectrum proportional to the base velocity and a smooth resonance peak around 1000 Hz with a -90° phase lag.

MASH2-0 electromechanical sigma-delta modulator for capacitive MEMS sensors using dual quantization method

Abstract: This paper presents a new control structure for an electromechanical sigma-delta modulator (EM-ΣΔM) based on the dual quantization technique. The modulator adopts a 2-0 multi-stage noise-shaping structure (MASH2-0), which was studied by system-level modeling and hardware implementation using an FPGA. The study shows that the MAH2-0, like the MASH2-2, is inherently stable, has a high overload-input level and high dynamic range compared to single-loop EM-ΣΔM. However, the MASH2-0, with its simpler implementation, achieved a higher dynamic range and better signal-to-noise ratio than a comparable MASH2-2 and fourth-order single-loop EM-ΣΔM. A capacitive MEMS accelerometer was designed and employed in this system. Within a bandwidth of 1 KHz, the sensor achieved a noise-floor level of -130 dB, a full scale of ±20g acceleration, and a bias instability of 20 μg for a period of three hours. The investigation confirms the concept of the MASH2-0 structure and shows its potential as a closed-loop interface for high-performance capacitive MEMS inertial sensors.

CMOS potentiostat and sensor with multilayer membrane for wide range measurements of glucose concentrations

Abstract: We report on an electrochemical measurement setup comprising a CMOS potentiostat and a glucose sensor with a two-layer membrane as the first steps towards the development of an integrated in-situ sensor system for bioreactors. The potentiostat has a chip size of 2.1 × 2.5 mm2 and a linear current range from -220 nA to 240 nA with a linearity of R2 = 0.9995. For wide range measurements of glucose concentrations in cell culture media, electrodes functionalized with the enzyme glucose oxidase were spin-coated with membranes made from polydimethylsiloxane (PDMS). With these membranes, glucose concentrations up to 400 mM were measured with a linear measurement range up to 100 mM. For interferent elimination, cellulose acetate membranes were employed.