Overcoming the Challenges for Multichip Integration: A Wireless Interconnect Approach

The physical limitations in the area, power density, and yield restrict the scalability of the single-chip multicore system to a relatively small number of cores. Instead of having a large chip, aggregating multiple smaller chips can overcome these physical limitations. Combining multiple dies can be done either by stacking vertically or by placing side-by-side on the same substrate within a single package. However, in order to be widely accepted, both multichip integration techniques need to overcome significant challenges. In the horizontally integrated multichip system, traditional inter-chip I/O does not scale well with technology scaling due to limitations of the pitch. Moreover, to transfer data between cores or memory components from one chip to another, state-of-the-art inter-chip communication over wireline channels require data signals to travel from internal nets to the peripheral I/O ports and then get routed over the inter-chip channels to the I/O port of the destination chip. Following this, the data is finally routed from the I/O to internal nets of the target chip over a wireline interconnect fabric. This multi-hop communication increases energy consumption while decreasing data bandwidth in a multichip system. On the other hand, in vertically integrated multichip system, the high power density resulting from the placement of computational components on top of each other aggravates the thermal issues of the chip leading to degraded performance and reduced reliability. Liquid cooling through microfluidic channels can provide cooling capabilities required for effective management of chip temperatures in vertical integration. However, to reduce the mechanical stresses and at the same time, to ensure temperature uniformity and adequate cooling competencies, the height and width of the microchannels need to be increased. This limits the area available to route Through-Silicon-Vias (TSVs) across the cooling layers and make the co-existence and co-design of TSVs and microchannels extreamly challenging. Research in recent years has demonstrated that on-chip and off-chip wireless interconnects are capable of establishing radio communications within as well as between multiple chips. The primary goal of this dissertation is to propose design principals targeting both horizontally and vertically integrated multichip system to provide high bandwidth, low latency, and energy efficient data communication by utilizing mm-wave wireless interconnects. The proposed solution has two parts: the first part proposes design methodology of a seamless hybrid wired and wireless interconnection network for the horizontally integrated multichip system to enable direct chip-to-chip communication between internal cores. Whereas the second part proposes a Wireless Network-on-Chip (WiNoC) architecture for the vertically integrated multichip system to realize data communication across interlayer microfluidic coolers eliminating the need to place and route signal TSVs through the cooling layers. The integration of wireless interconnect will significantly reduce the complexity of the co-design of TSV based interconnects and microchannel based interlayer cooling. Finally, this dissertation presents a combined trade-off evaluation of such wireless integration system in both horizontal and vertical sense and provides future directions for the design of the multichip system

Photovoltaic Energy Harvesting for Millimeter-Scale Systems

The Internet of Things (IoT) based on mm-scale sensors is a transformational technology that opens up new capabilities for biomedical devices, surveillance, micro-robots and industrial monitoring. Energy harvesting approaches to power IoT have traditionally included thermal, vibration and radio frequency. However, the achievement of efficient energy scavenging for IoT at the mm-scale or sub mm-scale has been elusive. In this work, I show that photovoltaic (PV) cells at the mm-scale can be an alternative means of wireless power transfer to mm-scale sensors for IoT, utilizing ambient indoor lighting or intentional irradiation of near-infrared (NIR) LED sources through biological tissue. Single silicon and GaAs photovoltaic cells at the mm-scale can achieve a power conversion efficiency of more than 17 % for silicon and 30 % for GaAs under low-flux NIR irradiation at 850 nm through the optimized device structure and sidewall/surface passivation studies, which guarantees perpetual operation of mm-scale sensors. Furthermore, monolithic single-junction GaAs photovoltaic modules offer a means for series-interconnected cells to provide sufficient voltage (> 5 V) for direct battery charging, and bypassing needs for voltage up-conversion circuitry. However, there is a continuing challenge to miniaturize such PV systems down to the sub mm-scale with minimal optical losses from device isolation and metal interconnects and efficient voltage up-conversion. Vertically stacked dual-junction PV cells and modules are demonstrated to increase the output voltage per cell and minimize area losses for direct powering of miniature devices for IoT and bio-implantable applications with low-irradiance narrowband spectral illumination. Dual-junction PV cells at small dimensions (150 µm x 150 µm) demonstrate power conversion efficiency greater than 22 % with more than 1.2 V output voltage under low-flux 850 nm NIR LED illumination, which is sufficient for batteryless operation of miniaturized CMOS IC chips. The output voltage of dual-junction PV modules with eight series-connected single cells is greater than 10 V while maintaining an efficiency of more than 18 %. Finally, I demonstrate monolithic PV/LED modules at the µm-scale for brain-machine interfaces, enabling two-way optical power and data transfer in a through-tissue configuration. The wafer-level assembly plan for the 3D vertical integration of three different systems including GaAs LED/PV modules, CMOS silicon chips, and neural probes is proposed.PHDElectrical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/163261/1/esmoon_1.pd

Implantable Neural Probes for Electrical Recording and Optical Stimulation of Cellular Level Neural Circuitry in Behaving Animals.

In order to advance the understanding of brain function, it is critical to monitor how neural circuits work together and perform computational processing. For the past few decades, a wide variety of neural probes have been developed to study the electrophysiology of the brain. This work is focused on two important objectives to improve the brain-computer interface: 1) to enhance the reliability of recording electrodes by optimizing the shank structure; 2) to incorporate optical stimulation capability in addition to electrical recording for applications involving optogenetics. For the first objective, a flexible 64-channel parylene probe was designed with unique geometries for reduced tissue reactions. In order to provide the mechanical stiffness necessary to penetrate the brain, the miniaturized, flexible probes were coated with a lithographically patterned silk fibroin, which served as a biodegradable insertion shuttle. Because the penetration strength is independent from the properties of the probe itself, the material and geometry of the probe structure can be optimally designed without constraints. These probes were successfully implanted into the layer-V of motor cortex in 6 rats and recorded neural activities in vivo for 6 weeks. For the second objective, either optical waveguides or μLEDs were monolithically integrated on the probe shanks for optogenetic applications. Compared to existing methods, this work can offer high spatial-temporal resolution to record and stimulate from even subcellular neural structures. In the experiments using wild type animals, despite optimized recording of spontaneous neural activities, the cells never responded to illumination. In contrast, for the ChR2 expressed animals, light activation of neural activities was extremely robust and local, which phase-locked to the light waveform whenever the cell was close to the light source. In particular, the probes integrated with μLEDs were capable of driving different neural circuit behaviors using two adjacent μLEDs separated only by a 60-μm-pitch. With 3 μLEDs integrated at the tip of each of the 4 probe shanks, this novel optogenetic probe can provide more than 480 million (12!) different spiking sequences at the sub-cellular resolution, which is ideal to manipulate high density neural network with versatility and precision.PhDElectrical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/111604/1/wufan_1.pd

Stepper microactuators driven by ultrasonic power transfer

Advances in miniature devices for biomedical applications are creating ever-increasing requirements for their continuous, long lasting, and reliable energy supply, particularly for implanted devices. As an alternative to bulky and cost inefficient batteries that require occasional recharging and replacement, energy harvesting and wireless power delivery are receiving increased attention. While the former is generally only suited for low-power diagnostic microdevices, the latter has greater potential to extend the functionality to include more energy demanding therapeutic actuation such as drug release, implant mechanical adjustment or microsurgery. This thesis presents a novel approach to delivering wireless power to remote medical microdevices with the aim of satisfying higher energy budgets required for therapeutic functions. The method is based on ultrasonic power delivery, the novelty being that actuation is powered by ultrasound directly rather than via piezoelectric conversion. The thesis describes a coupled mechanical system remotely excited by ultrasound and providing conversion of acoustic energy into motion of a MEMS mechanism using a receiving membrane coupled to a discrete oscillator. This motion is then converted into useful stepwise actuation through oblique mechanical impact. The problem of acoustic and mechanical impedance mismatch is addressed. Several analytical and numerical models of ultrasonic power delivery into the human body are developed. Major design challenges that have to be solved in order to obtain acceptable performance under specified operating conditions and with minimum wave reflections are discussed. A novel microfabrication process is described, and the resulting proof-of-concept devices are successfully characterized.Open Acces

Low Power Autonomous Microsystem for Oil Well Logging Applications

Downhole environmental monitoring can provide significant benefits to the petroleum industry. The rapid development of semiconductor technology enables autonomous sensing microsystems to operate at extreme environments. By injecting these microsystems into the boreholes and retrieving them after deployment, the geophysical conditions in the area of interest can be obtained. Challenges include high temperature, high pressure, miniaturized system size and packaging. This dissertation describes three generations of the environmental logging microsystem (ELM) for downhole geophysical logging applications. The first generation of the microsystem, ELM1.0, is designed for temperature logging in downhole environments. Each system consists of a power management circuit, a microcontroller with an integrated temperature sensor, and optical indicators. The system electronics are integrated on a flexible printed circuit board and packaged in a steel shell. The ELM1.0 has a packaged size of 8.9×8.9×6.85 mm3. It was tested at up to 125°C, 50 MPa in high salinity condition. The second generation (ELM2.0 & ELM2.1) is upgraded from ELM1.0 by adding a micromachined capacitive pressure sensor for pressure sensing up to 50 MPa. The ELM2.0 & ELM2.1 systems are packaged in steel shells filled with transparent polymer for pressure transfer. The packaged systems have a dimension of 9.5×9.5×6.5 mm3. The third generation (ELM3.0) is upgraded from ELM2.0 with a power switch and a low-cost polyimide pressure sensor for coarse pressure measurement up to 50 MPa. Both ELM2.0 and ELM3.0 systems were successfully tested at up to 125°C, 50 MPa in corrosive environments using laboratory instruments, and in a brine well at a depth up to 1235 m. A progressive polynomial calibration method was used for interpretation of the pressure sensor data from these tests. In addition, a high power micromachined RF switch for radio transceiver applications was designed, fabricated and tested. The RF switch can potentially be used to establish antenna networks for RF communication in the ELM. The switch consists of a bridge structure for electrostatic actuation and capacitive contact. The switch was fabricated with a 7-mask process. The fabricated device showed limited RF performance because of challenges related to the control of residual stress in suspended elements.PHDElectrical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttps://deepblue.lib.umich.edu/bitstream/2027.42/138647/1/sui_1.pd

System-level design and RF front-end implementation for a 3-10ghz multiband-ofdm ultrawideband receiver and built-in testing techniques for analog and rf integrated circuits

This work consists of two main parts: a) Design of a 3-10GHz UltraWideBand (UWB) Receiver and b) Built-In Testing Techniques (BIT) for Analog and RF circuits. The MultiBand OFDM (MB-OFDM) proposal for UWB communications has received significant attention for the implementation of very high data rate (up to 480Mb/s) wireless devices. A wideband LNA with a tunable notch filter, a downconversion quadrature mixer, and the overall radio system-level design are proposed for an 11-band 3.4-10.3GHz direct conversion receiver for MB-OFDM UWB implemented in a 0.25mm BiCMOS process. The packaged IC includes an RF front-end with interference rejection at 5.25GHz, a frequency synthesizer generating 11 carrier tones in quadrature with fast hopping, and a linear phase baseband section with 42dB of gain programmability. The receiver IC mounted on a FR-4 substrate provides a maximum gain of 67-78dB and NF of 5-10dB across all bands while consuming 114mA from a 2.5V supply. Two BIT techniques for analog and RF circuits are developed. The goal is to reduce the test cost by reducing the use of analog instrumentation. An integrated frequency response characterization system with a digital interface is proposed to test the magnitude and phase responses at different nodes of an analog circuit. A complete prototype in CMOS 0.35mm technology employs only 0.3mm2 of area. Its operation is demonstrated by performing frequency response measurements in a range of 1 to 130MHz on 2 analog filters integrated on the same chip. A very compact CMOS RF RMS Detector and a methodology for its use in the built-in measurement of the gain and 1dB compression point of RF circuits are proposed to address the problem of on-chip testing at RF frequencies. The proposed device generates a DC voltage proportional to the RMS voltage amplitude of an RF signal. A design in CMOS 0.35mm technology presents and input capacitance <15fF and occupies and area of 0.03mm2. The application of these two techniques in combination with a loop-back test architecture significantly enhances the testability of a wireless transceiver system

Design, manufacturing and characterisation of a wireless flexible pressure sensor system for the monitoring of the gastro-intestinal tract

Ingestible motility capsule (IMC) endoscopy holds a strong potential in providing advanced diagnostic capabilities within the small intestine with higher patient tolerance for pathologies such as irritable bowel syndrome, gastroparesis and chronic abdominal amongst others. Currently state-of-the art IMCs are limited by the use of obstructive off-the-shelf sensing modules that are unable to provide multi-site tactile monitoring of the Gastro-Intestinal tract. In this work a novel 12 mm in diameter by 30 mm in length IMC is presented that utilises custom-built flexible, thin-film, biocompatible, wireless and highly sensitive tactile pressure sensors arrays functionalising the capsule shell. The 150 μm thick, microstructured, PDMS flexible passive pressure sensors are wirelessly powered and interrogated, and are capable of detecting pressure values ranging from 0.1 kPa up to 30 kPa with a 0.1 kPa resolution. A novel bottom-up wafer-scale microfabrication process is presented which enables the development of these ultra-dense, self-aligned, scalable and uniquely addressable flexible wireless sensors with high yield (>80%). This thesis also presents an innovative metallisation microfabrication process on soft-elastomeric substrates capable to withstand without failure of the tracks 180o bending, folding and iterative deformation such as to allow conformable mapping of these sensors. A custom-built and low-cost reflectometer system was also designed, built and tested within the capsule that can provide a fast (100 ms) and accurate extraction (±0.1 kPa) of their response. In vitro and in vivo characterisation of the developed IMC device is also presented, facilitated respectively via the use of a biomimetic phantom gut and via live porcine subjects. The capsule device was found to successfully capture respiration, low-amplitude and peristaltic motility of the GI tract from multiple sites of the capsule.UK Engineering & Physical Sciences Research Council (EPSRC) through the Programme Grant Sonopill (EP/K034537/2)James Watt Scholarshi

A review of advances in pixel detectors for experiments with high rate and radiation

The Large Hadron Collider (LHC) experiments ATLAS and CMS have established hybrid pixel detectors as the instrument of choice for particle tracking and vertexing in high rate and radiation environments, as they operate close to the LHC interaction points. With the High Luminosity-LHC upgrade now in sight, for which the tracking detectors will be completely replaced, new generations of pixel detectors are being devised. They have to address enormous challenges in terms of data throughput and radiation levels, ionizing and non-ionizing, that harm the sensing and readout parts of pixel detectors alike. Advances in microelectronics and microprocessing technologies now enable large scale detector designs with unprecedented performance in measurement precision (space and time), radiation hard sensors and readout chips, hybridization techniques, lightweight supports, and fully monolithic approaches to meet these challenges. This paper reviews the world-wide effort on these developments.Comment: 84 pages with 46 figures. Review article.For submission to Rep. Prog. Phy

Design, characterization and testing of a thin-film microelectrode array and signal conditioning microchip for high spatial resolution surface laplacian measurement.

Cardiac mapping has become an important area of research for understanding the mechanisms responsible for cardiac arrhythmias and the associated diseases. Current technologies for measuring electrical potentials on the surface of the heart are limited due to poor spatial resolution, localization issues, signal distortion due to noise, tissue damage, etc. Therefore, the purpose of this study is to design, develop, characterize and investigate a custom-made microfabricated, polyimide-based, flexible Thin-Film MicroElectrode Array (TFMEA) that is directly interfaced to an integrated Signal Conditioning Microchip (SCM) to record cardiac surface potentials on the cellular level to obtain high spatial resolution Surface Laplacian (SL) measurement. TFMEAs consisting of five fingers (Cover area = 4 mm2 and 16 mm2), which contained five individual microelectrodes placed in orthogonal directions (25-µm in diameter, 75-µm interelectrode spacing) to one another, were fabricated within a flexible polyimide substrate and capable of recording electrical activities of the heart on the order of individual cardiomyocytes. A custom designed SCM consisting of 25 channels of preamplification stages and second order band-pass filters was interfaced directly with the TFMEA in order to improve the signal-to-noise ratio (SNR) characteristics of the high spatial resolution recording data. Metrology characterization using surface profilometry and high resolution Scanning Electron Microscope (SEM) indicated the geometry of fabricated TFMEAs closely matched the design parameters \u3c 0.4%). The DC resistances of the 25 individual micro electrodes were consistent (1.050 ± 0.026 kO). The simulation and testing results of the SCM verified the pre-amplification and filter stages met the designed gain and frequency parameters within 2.96%. The functionality of the TFMEA-SCM system was further characterized on a TX 151 conductive gel. The characterization results revealed that the system functionality was sufficient for high spatial cardiac mapping. In vivo testing results clearly demonstrated feasibility of using the TFMEA-SCM system to obtain cellular level SL measurements with significantly improved the SNRs during normal sinus rhythm and Ventricular Fibrillation (VF). Local activation times were detected via evaluating the zero crossing of the SL electro grams, which coincided with the gold standard (dV/dt)min of unipolar electro grams within ± 1%. The in vivo transmembrane current densities calculated from the high spatial resolution SLs were found to be significantly higher than the transmembrane current densities computed using electrodes with higher interelectrode spacings. In conclusion, the custom-made TFMEASCM systems demonstrated feasibility as a tool for measuring cardiac potentials and to perform high resolution cardiac mapping experiments

Low power CMOS IC, biosensor and wireless power transfer techniques for wireless sensor network application

The emerging field of wireless sensor network (WSN) is receiving great attention due to the interest in healthcare. Traditional battery-powered devices suffer from large size, weight and secondary replacement surgery after the battery life-time which is often not desired, especially for an implantable application. Thus an energy harvesting method needs to be investigated. In addition to energy harvesting, the sensor network needs to be low power to extend the wireless power transfer distance and meet the regulation on RF power exposed to human tissue (specific absorption ratio). Also, miniature sensor integration is another challenge since most of the commercial sensors have rigid form or have a bulky size. The objective of this thesis is to provide solutions to the aforementioned challenges