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The parallelization of intracellular recording can greatly benefit the study of complex neuronal networks, but it has proven difficult to achieve. To meet this challenge, we have been developing large-scale arrays of intracellular vertical nanoscale electrodes operated by underlying CMOS integrated circuits. The development has been fruitful, and our first-generation CMOS nanoelectrode array hit a milestone by intracellularly recording from up to 235 networked cardiomyocytes in parallel. We reported this first-generation system and its unprecedented parallelism in intracellular recording in Nature Nanotechnology 12, 460 (2017). The present paper is a review of this work with a special focus on the development of its CMOS integrated circuit.

Electrode technology for electrophysiology has a long history of innovation, with some decisive steps including the development of the voltage-clamp measurement technique by Hodgkin and Huxley in the 1940s and the invention of the patch clamp electrode by Neher and Sakmann in the 1970s. The high-precision intracellular recording enabled by the patch clamp electrode has since been a gold standard in studying the fundamental cellular processes underlying the electrical activities of neurons and other excitable cells. One logical next step would then be to parallelize these intracellular electrodes, since simultaneous intracellular recording from a large number of cells will benefit the study of complex neuronal networks and will increase the throughput of electrophysiological screening from basic neurobiology laboratories to the pharmaceutical industry. Patch clamp electrodes, however, are not built for parallelization; as for now, only ∼10 patch measurements in parallel are possible. It has long been envisioned that nanoscale electrodes may help meet this challenge. First, nanoscale electrodes were shown to enable intracellular access. Second, because their size scale is within the normal reach of the standard top-down fabrication, the nanoelectrodes can be scaled into a large array for parallelization. Third, such a nanoelectrode array can be monolithically integrated with complementary metal-oxide semiconductor (CMOS) electronics to facilitate the large array operation and the recording of the signals from a massive number of cells. These are some of the central ideas that have motivated the research activity into nanoelectrode electrophysiology, and these past years have seen fruitful developments. This Account aims to synthesize these findings so as to provide a useful reference. Summing up from the recent studies, we will first elucidate the morphology and associated electrical properties of the interface between a nanoelectrode and a cellular membrane, clarifying how the nanoelectrode attains intracellular access. This understanding will be translated into a circuit model for the nanobio interface, which we will then use to lay out the strategies for improving the interface. The intracellular interface of the nanoelectrode is currently inferior to that of the patch clamp electrode; reaching this benchmark will be an exciting challenge that involves optimization of electrode geometries, materials, chemical modifications, electroporation protocols, and recording/stimulation electronics, as we describe in the Account. Another important theme of this Account, beyond the optimization of the individual nanoelectrode-cell interface, is the scalability of the nanoscale electrodes. We will discuss this theme using a recent development from our groups as an example, where an array of ca. 1000 nanoelectrode pixels fabricated on a CMOS integrated circuit chip performs parallel intracellular recording from a few hundreds of cardiomyocytes, which marks a new milestone in electrophysiology.

The dispersion relation of plasmons in graphene with a periodic lattice of apertures takes a band structure. Light incident on this plasmonic crystal excites only particular plasmonic modes in select bands. The selection rule is not only frequency/wavevector matching but also symmetry matching, where the symmetry of plasmonic modes originates from the point group symmetry of the lattice. We demonstrate versatile manipulation of light-plasmon coupling behaviors by engineering the symmetry of the graphene plasmonic crystal.

This special issue features twelve selected papers from ISSCC 2015, held in San Francisco, CA, from February 22–26, 2015.

In this chapter, we reported several portable nuclear magnetic resonance (NMR) systems implemented with silicon integrated circuits (IC). Being the initial researchers in the NMR on IC field, we firstly proposed to integrate the complex NMR electronics with the customized IC for portable NMR application with a palm size magnet. Moreover, to manage the samples inside the narrow opening of the portable magnet, we proposed the integration of the digital microfluidic device with the portable NMR system to attain electronic-automated multi-sample management scheme. With the capacitive sensing module of the droplets, the samples can be guided to the NMR sensing site sequentially to reduce labor and experimental time, which facilitates the detection and supports high-throughput sensing. Lastly, we demonstrates a NMR system with magnetic field calibration. This calibration culminates in a robust NMR sensing scheme by modulating the actual magnetic field to a steady value. Thus, the Larmor frequency can be stabilized, and the NMR sensing can work at different environment.

This paper reviews our portable multi-dimensional nuclear magnetic resonance (NMR) spectroscopy system combining a 4-mm2 CMOS NMR spectrometer integrated circuit (IC) and a permanent magnet. The work was first reported in [1] with emphases on overall system development and spectroscopy experimentations. Here we pay more attention to the IC design. The scalability of the integrated spectrometer can enable not only portable NMR spectroscopy in conjunction with small permanent magnets for in-field and online applications, but also parallel NMR spectroscopy for high-throughput applications.

Optical methods based on voltage sensitive proteins and Ca2+/voltage sensitive dyes have significantly benefited the field of electrophysiology, parallelizing intracellular recording from a network of electrogenic cells. Creating an analogous all-electrical device — an electrode array capable of intracellular recording from a network of electrogenic cells — has long been an outstanding challenge. On the one hand, though the CMOS microelectrode array has enabled network-level studies with massive parallelism, its extracellular interface has a limited sensitivity. On the other hand, planar patch clamp arrays achieve intracellular access but are not applicable to network-level interrogations. We will present our recent development of a CMOS nanoelectrode array that combines both parallel and intracellular features for high-precision recording across a large network of electrogenic cells, and its outlooks in neurobiology and cardiology.

Electrical sensing of biomolecules has been an important pursuit due to the label-free operation and chip-scale construct such sensing modality can enable. In particular, electrical biomolecular sensors based on nanomaterials such as semiconductor nanowires, carbon nanotubes, and graphene have demonstrated high sensitivity, which in the case of nanowires and carbon nanotubes can surpass typical optical detection sensitivity. Among these nanomaterials, graphene is well suited for a practical candidate for implementing a large-scale array of biomolecular sensors, as its two-dimensional morphology is readily compatible with industry standard top-down fabrication techniques. In our recent work published in 2014 Nature Communications, we demonstrated these benefits by creating DNA sensor arrays from chemical vapor deposition (CVD) graphene. The present chapter, which is a review of this recent work, outlines procedures demonstrating the use of individual graphene sites of the array in dual roles--electrophoretic electrodes for site specific probe DNA immobilization and field effect transistor (FET) sensors for detection of target DNA hybridization. The 100 fM detection sensitivity achieved in 7 out of 8 graphene FET sensors in the array combined with the alternative use of the graphene channels as electrophoretic electrodes for probe deposition represent steps toward creating an all-electrical multiplexed DNA array.

Electrical sensing of biomolecules has been an important pursuit due to the label-free operation and chip-scale construct such sensing modality can enable. In particular, electrical biomolecular sensors based on nanomaterials such as semiconductor nanowires, carbon nanotubes, and graphene have demonstrated high sensitivity, which in the case of nanowires and carbon nanotubes can surpass typical optical detection sensitivity. Among these nanomaterials, graphene is well suited for a practical candidate for implementing a large-scale array of biomolecular sensors, as its two-dimensional morphology is readily compatible with industry standard top-down fabrication techniques. In our recent work published in 2014 Nature Communications, we demonstrated these benefits by creating DNA sensor arrays from chemical vapor deposition (CVD) graphene. The present chapter, which is a review of this recent work, outlines procedures demonstrating the use of individual graphene sites of the array in dual roles--electrophoretic electrodes for site specific probe DNA immobilization and field effect transistor (FET) sensors for detection of target DNA hybridization. The 100 fM detection sensitivity achieved in 7 out of 8 graphene FET sensors in the array combined with the alternative use of the graphene channels as electrophoretic electrodes for probe deposition represent steps toward creating an all-electrical multiplexed DNA array.

By combining the physics of nuclear magnetic resonance (NMR) and silicon radio-frequency (RF) integrated circuits, we recently created progressively smaller NMR systems, which we originally reported in Refs. [1] , [2] , [3] , [4] . Our strategy for NMR system miniaturization proved effective, culminating in the smallest prototype [3] , [4] that weighs 0.1 kg and can be held at the palm of the hand. These small, low-cost NMR systems can be useful as biomolecular sensors in the personalized medicine setting, and we demonstrated their ability to detect proteins, compounds, and human cancer cells. The present paper, which is not a new technical contribution, reviews these developments.

We report on CMOS temperature sensors that work by measuring temperature-dependent delays in CMOS inverters. Two new features distinguish this work from the prior delay-based temperature sensors. First, our sensor operates with simple, low-cost one-point calibration. Second, it uses delay-locked loops (DLLs) to convert inverter delays to digital temperature outputs: the use of DLLs enables low energy (0.24 μJ/sample) and high bandwidth (5 kilo-samples/s), facilitating fast thermal monitoring. After calibration, measurement errors for 15 chips fabricated in digital CMOS 0.13 μm fall within -4.0~4.0 °C in a temperature range of 0~100 °C, where the temperature chamber used has a control uncertainty of ±1.1 °C. Microprocessor thermal profiling can be a potential application.

In our earlier work, we developed a 2-kg NMR system, which was 60 X lighter, 40× smaller, yet 60× more spin-mass sensitive than a 120-kg state-of-the-art commercial benchtop system. Here we report on two new nuclear magnetic resonance (NMR) systems that represent further orders-of-magnitude size reduction and lab-on-a-chip capability. The first system, which weighs 0.1 kg and can be held in the palm of a hand, is the smallest NMR system ever built, and is 1200× lighter, 1200× smaller, yet 150× more spin-mass sensitive than the commercial system. It is enabled by combining the physics of NMR with a CMOS RF transceiver. The second system, which even integrates a sample coil, directly interfaces the CMOS chip with a sample for lab-on-a-chip operation. The two systems detect biological objects such as avidin, human chorionic gonadotropin, and human bladder cancer cells.

In distributed oscillators, a large or infinite number of voltage and current variables that represent an oscillating electromagnetic wave are perturbed by distributed noise sources to result in phase noise. Here we offer an explicit, physically intuitive analysis of the seemingly complex phase-noise process in distributed oscillators. This study, confirmed by experiments, shows how the phase noise varies with the shape and physical nature of the oscillating electromagnetic wave, providing design insights and physical understanding.

www.MaterialsViews.com C O M Stretchable Microfl uidic Radiofrequency Antennas M U N I By Masahiro Kubo , Xiaofeng Li , Choongik Kim , Michinao Hashimoto , Benjamin J. Wiley , Donhee Ham , and George M. Whitesides * C A IO N This paper describes a new method for fabricating stretchable radiofrequency antennas. The antennas consist of liquid metal (eutectic gallium indium alloy, EGaIn [ 1 , 2 ] ) enclosed in elastomeric microfl uidic channels. In particular, a microfl uidic structure made of two types of elastomers (polydimethylsiloxane (PDMS) and Ecofl ex (type 0030, Reynolds Advanced Materials)) with different stiffness has been developed to improve the stretchability and mechanical stability of the antennas. These antennas can be stretched up to a strain [defi ned as the percentage change in length or ( l – l 0 )/ l 0 ] of 120 %. This high stretchability allows the resonance frequencies of the antennas to be mechanically tuned over a wide range of frequencies. The antennas can also be repeatedly stretched, while retaining a high effi ciency (> 95 %) in radiation. “Stretchability” in electronics has the potential to open new opportunities, particularly for large-area devices and systems, and in systems that require the device to conform to a nonplanar surface, or to bend and stretch while in use. [ 3–5 ] Compared to “fl exible” electronics built on nonstretchable polymer or paper substrates, [ 6 , 7 ] stretchable electronics can cover almost arbitrarily curved surfaces and movable parts. Mechanical compliance may increase the comfort of the user for wearable electronics or implantable medical devices, and simplify the integration for a range of applications. [ 3–5 , 8 ] New approaches to stretchable electronics are now being developed. In a recent advance, Rogers et al. [ 4 , 5 ] described stretchable integrated circuits with elongation of up to 100 % using wavy, thin silicon ribbons on pre-stretched elastic substrates. Antennas offer new, attractive applications for stretchable electronics; these applications might include reconfi gurable antennas, [ 9 ] antennas for limited and nonplanar spaces, [ 10 ] and wearable sensors. Two methods are commonly used to build antennas for commercial applications. The most common method uses sheet-metal processing; in this method, a metal sheet is punched, bent, and welded into the desired structure. A second method uses chemical etching and plating to make small patterns of metal. This method can make fl exible antennas by patterning metal on a fl exible substrate. Neither

Three-dimensional (3D), multi-transistor-layer, integrated circuits represent an important technological pursuit promising advantages in integration density, operation speed, and power consumption compared with 2D circuits. We report fully functional, 3D integrated complementary metal-oxide-semiconductor (CMOS) circuits based on separate interconnected layers of high-mobility n-type indium arsenide (n-InAs) and p-type germanium/silicon core/shell (p-Ge/Si) nanowire (NW) field-effect transistors (FETs). The DC voltage output ( V out ) versus input ( V in ) response of vertically interconnected CMOS inverters showed sharp switching at close to the ideal value of one-half the supply voltage and, moreover, exhibited substantial DC gain of ≈45. The gain and the rail-to-rail output switching are consistent with the large noise margin and minimal static power consumption of CMOS. Vertically interconnected, three-stage CMOS ring oscillators were also fabricated by using layer-1 InAs NW n-FETs and layer-2 Ge/Si NW p-FETs. Significantly, measurements of these circuits demonstrated stable, self-sustained oscillations with a maximum frequency of 108 MHz, which represents the highest-frequency integrated circuit based on chemically synthesized nanoscale materials. These results highlight the flexibility of bottom-up assembly of distinct nanoscale materials and suggest substantial promise for 3D integrated circuits.

We report on an electrical oscillator that self-generates a periodic train of short-duration pulses. The oscillator consists of a nonlinear transmission line (NLTL), one end of which is connected to a one-port amplifier and the other end is open. In the steady state, a self-generated short-duration pulse travels back and forth on the NLTL, reflected at both ends of the NLTL due to impedance mismatches. The one-port amplifier produces a negative output resistance for a voltage beyond a particular threshold and a positive output resistance for a voltage below that threshold, and thus, the reflection from the amplifier provides gain for the main upper portion of the pulse to compensate loss, and attenuates small perturbations to ensure oscillation stability. The NLTL substantially sharpens the pulse.

We report on a CMOS RF transceiver designed for detection of biological objects such as cancer marker proteins. Its main function is to manipulate and monitor RF dynamics of protons in water via nuclear magnetic resonance (NMR). Target objects alter the proton dynamics, which is the basis for our biosensing. The RF transceiver has a measured receiver noise figure of 0.7 dB. This high sensitivity enabled construction of an entire NMR system around the RF transceiver in a 2-kg portable platform, which is 60 times lighter, 40 times smaller, yet 60 times more mass sensitive than a state-of-the-art commercial benchtop system. Sensing 20 fmol and 1.4 ng of avidin (protein) in a 5 muL sample volume, our system represents a circuit designer's approach to pursue low-cost diagnostics in a portable platform.

The 29 papers in this special issue are drawn from the IEEE International Solid-State Circuits Conference (ISSCC), held in San Francisco, CA, February 3-7, 2008.

The authors demonstrate 1.6GHz surface acoustic wave (SAW) generation using interdigital transducers patterned by e-beam lithography on a thin ZnO piezoelectric film deposited on an InP substrate. The highly oriented, dense, and fine-grain ZnO film with high resistivity was deposited by radio frequency magnetron sputtering and was characterized by x-ray diffraction, scanning electron microscopy, atomic force microscopy, and a four-point probe station. The acoustic wavelength of the 1.6GHz SAW generated by exciting the interdigital transducer on ZnO∕InP with a microwave signal is 1.6μm. This SAW filter device could be monolithically integrated with optoelectronic devices, opening new opportunities to use SAWs for applications such as gigahertz-frequency filters on optoelectronic devices and novel widely tunable quantum cascade lasers.

We review three examples (an on-chip transmission line resonator [1], a phase-locked loop [2], and an analog-to-digital converter [3]) of design tradeoffs which can in fact be circumvented; the key in each case is that the parameters that seem to trade off with each other are actually separated in time or space. This paper is an attempt to present these designs in such a way that this common approach can hopefully be applied to other circuits. We note reader that this paper is not a new contribution, but a review in which we highlight the common theme from our published works [1-3]. We published a similar paper [4], which, however, used only two examples from [1] and [2]. With the newly added content from [3] in the list of our examples, the present paper offers an expanded scope.

We propose a new digital background calibration method for capacitor mismatches in pipelined analog-to-digital converters (ADCs). It combines commutated feedback capacitor switching with a background digital correlation loop to extract capacitor mismatch information, which is subsequently used to correct errors caused by the mismatch. This is an all-digital technique requiring minimal extra digital circuits, and is applicable to both single-bit and multibit-per-stage architectures. Simulations with a 15-stage, 1.5-bit-per-stage pipelined ADC with capacitor mismatch of sigma = 0.25% in each stage show that the technique improves signal-to-noise-distortion ratio from 62 dB (10 bits) to 94 dB (15.4 bits).

We introduce a single-loop PLL that operates in a narrower-bandwidth, integer-N mode during phase lock and in a wider-bandwidth, fractional-N mode during transient. This hybrid PLL, as a generalization of the conventional variable-bandwidth PLL that shifts only its bandwidth, simultaneously achieves the fast-locking advantage of the fractional-N PLL and design simplicity of the integer-N PLL, and as such, brings benefits in certain important PLL applications. In addition, the frequency division mode switching, unique in the hybrid PLL, enables a new, more digital protocol to execute bandwidth switching. A CMOS IC prototype attests to the validity of the proposed approach.

The nonlinear transmission line is a structure where short-duration pulses called electrical solitons can be created and propagated. By combining, in a closed-loop topology, the nonlinear line and a special amplifier that provides not only gain but also mechanisms to tame inherently unruly soliton dynamics, we recently constructed the first electrical soliton oscillator that self-generates a stable, periodic train of electrical soliton pulses (Ricketts , IEEE Trans. MTT, 2006). This paper starts with a review of this recently introduced circuit concept, and then reports on new contributions, i.e., further experimental studies of the dynamics of the stable soliton oscillator and a CMOS prototype demonstrating the chip-scale operation of the stable soliton oscillator. Finally, we go to the opposite end of the spectrum and present a numerical study showing the possibilities that deliberate promotions of the unruly soliton dynamics in the closed-loop topology can produce chaotic signals.

The silicon microelectronic chips that make today's computers possible are emerging as powerful tools for rapid and sensitive analysis of small biological objects, including cells, proteins, DNA, and viruses. Major new and exciting developments in the interface of solid-state circuits and biological entities are discussed in this article.

We recently integrated all major functions – RF transmitter, RF receiver, and arbitrary pulse sequencer – of the conventionally bulky NMR spectrometer electronics into a fingertip-sized silicon chip and demonstrated various multidimensional NMR spectroscopy experiments with them, using various bio- and organic molecules. We envision that the size and cost economy of such integrated spectrometer chips can open up new exciting vistas in the science and technology of NMR. For example, high-throughput structural analysis of macromolecules can be enabled by operating a large number of the spectrometer chips in parallel inside a high-field superconducting magnet. For another example, online, on-site small-molecule analysis can be performed in a miniaturized, thus portable, platform that combines a spectrometer chip with a low-field compact permanent magnet. In this article, we will discuss the technical background and outlook of this recent synergy between semiconductor chip technology and NMR science. Keywords: NMR spectroscopy; multidimensional NMR spectroscopy; semiconductor; semiconductor chips; integrated circuits

By combining the physics of nuclear magnetic resonance (NMR) and silicon radio-frequency (RF) integrated circuits, we recently created progressively smaller NMR systems, which have been reported in references 1–4. Our strategy for NMR system miniaturization proved effective, culminating in the smallest prototype that weighs 0.1 kg and can be held in the palm of the hand. These small, low-cost NMR systems can be useful as biomolecular sensors in the personalized medicine setting, and we demonstrated their ability to detect proteins, compounds, and human cancer cells. The chapter reviews these developments. Portions of this chapter are reprinted from our recent review paper of with permission.

While the use of sinusoidal electromagnetic waves as information carriers is taken as one of the principal axioms of today's wireless system design, certain nonsinusoidal waves may further enrich the scope and capacity of modern wireless engineering. Two notable nonsinusoid examples are impulses and chaotic signals. The short temporal width of impulses has enabled applications such as ranging radars and ultra wideband (UWB). The complex nature of chaotic signals offers a new means of encrypted communication. Here we review a new circuit paradigm, the electrical soliton oscillator, which can self-generate both impulse and chaotic signals of very large bandwidth by leveraging the singular dynamics of a nonlinear wave known as the electrical soliton. By combining a nonlinear transmission line with a unique amplifier that can "tame" the inherently unruly dynamics of solitons, the oscillator self-generates a stable, periodic train of short impulses. If the taming functions of the amplifier are turned off, the circuit self-generates chaotic signals by positively exploiting solitons' unruly nature. While still in its early stages, this soliton circuit may one day serve as the heartbeat of both impulse and chaotic wireless systems

This paper introduces an integrated circuit (IC)/microfluidic hybrid system for magnetic manipulation of biological cells. The hybrid system consists of an IC and a microfluidic system fabricated on top. Biological cells attached to magnetic beads are suspended inside the microfluidic system that maintains biocompatibility. The IC contains a microcoil array circuit that produces spatially-patterned microscopic magnetic fields. Programmable, rapid reconfiguration of the field pattern made possible by the IC allows an efficient simultaneous manipulation of multiple individual bead-bound cells with precise position control. Two prototypes, SiGe/microfluidic and CMOS/microfluidic hybrid systems, validate the proposed approach.

This paper introduces the first robust self-sustained electrical soliton oscillator. It self-starts by amplifying background noise to produce a stable train of periodic electrical soliton pulses. The oscillator is made possible by coupling a nonlinear transmission line with a unique amplifier that tames the instability-prone soliton dynamics. Two experimental prototypes, built at the discrete level, fully demonstrate the detailed operation of the circuit. The soliton oscillator is an electrical analog of optical soliton mode-locked systems

This paper presents a new physical theory of oscillator phase noise. Built around the concept of phase diffusion, this work bridges the fundamental physics of noise and existing oscillator phase-noise theories. The virtual damping of an ensemble of oscillators is introduced as a measure of phase noise. The explanation of linewidth compression through virtual damping provides a unified view of resonators and oscillators. The direct correspondence between phase noise and the Einstein relation is demonstrated, which reveals the underlying physics of phase noise. The validity of the new approach is confirmed by consistent experimental agreement.

Radio-frequency (RF) electronics, which combine passive electromagnetic devices and active transistors to generate and process gigahertz (GHz) signals, provide a critical basis of ever-pervasive wireless networks. While transistors are best realized by top-down fabrication, relatively larger electromagnetic passives are within the reach of printing techniques. Here, direct writing of viscoelastic silver-nanoparticle inks is used to produce a broad array of RF passives operating up to 45 GHz. These include lumped devices such as inductors and capacitors, and wave-based devices such as transmission lines, their resonant networks, and antennas. Moreover, to demonstrate the utility of these printed RF passive structures in active RF electronic circuits, they are combined with discrete transistors to fabricate GHz self-sustained oscillators and synchronized oscillator arrays that provide RF references, and wireless transmitters clocked by the oscillators. This work demonstrates the synergy of direct ink writing and RF electronics for wireless applications.

Field-effect transistor biomolecular sensors based on low-dimensional nanomaterials boast sensitivity, label-free operation and chip-scale construction. Chemical vapour deposition graphene is especially well suited for multiplexed electronic DNA array applications, since its large two-dimensional morphology readily lends itself to top-down fabrication of transistor arrays. Nonetheless, graphene field-effect transistor DNA sensors have been studied mainly at single-device level. Here we create, from chemical vapour deposition graphene, field-effect transistor arrays with two features representing steps towards multiplexed DNA arrays. First, a robust array yield--seven out of eight transistors--is achieved with a 100-fM sensitivity, on par with optical DNA microarrays and at least 10 times higher than prior chemical vapour deposition graphene transistor DNA sensors. Second, each graphene acts as an electrophoretic electrode for site-specific probe DNA immobilization, and performs subsequent site-specific detection of target DNA as a field-effect transistor. The use of graphene as both electrode and transistor suggests a path towards all-electrical multiplexed graphene DNA arrays.

State-of-the-art NMR spectrometers using superconducting magnets have enabled, with their ultrafine spectral resolution, the determination of the structure of large molecules such as proteins, which is one of the most profound applications of modern NMR spectroscopy. Many chemical and biotechnological applications, however, involve only small-to-medium size molecules, for which the ultrafine resolution of the bulky, expensive, and high-maintenance NMR spectrometers is not required. For these applications, there is a critical need for portable, affordable, and low-maintenance NMR spectrometers to enable in-field, on-demand, or online applications (e.g., quality control, chemical reaction monitoring) and co-use of NMR with other analytical methods (e.g., chromatography, electrophoresis). As a critical step toward NMR spectrometer miniaturization, small permanent magnets with high field homogeneity have been developed. In contrast, NMR spectrometer electronics capable of modern multidimensional spectroscopy have thus far remained bulky. Complementing the magnet miniaturization, here we integrate the NMR spectrometer electronics into 4-mm(2) silicon chips. Furthermore, we perform various multidimensional NMR spectroscopies by operating these spectrometer electronics chips together with a compact permanent magnet. This combination of the spectrometer-electronics-on-a-chip with a permanent magnet represents a useful step toward miniaturization of the overall NMR spectrometer into a portable platform.

We introduce far-infrared graphene plasmonic crystals. Periodic structural perturbation—in a proof-of-concept form of hexagonal lattice of apertures—of a continuous graphene medium alters delocalized plasmonic dynamics, creating plasmonic bands in a manner akin to photonic crystals. Fourier transform infrared spectroscopy demonstrates band formation, where far-infrared irradiation excites a unique set of plasmonic bands selected by phase matching and symmetry-based selection rules. This band engineering may lead to a new class of graphene plasmonic devices.

A wealth of effort in photonics has been dedicated to the study and engineering of surface plasmonic waves in the skin of three-dimensional bulk metals, owing largely to their trait of subwavelength confinement. Plasmonic waves in two-dimensional conductors, such as semiconductor heterojunction and graphene, contrast the surface plasmonic waves on bulk metals, as the former emerge at gigahertz to terahertz and infrared frequencies well below the photonics regime and can exhibit far stronger subwavelength confinement. This review elucidates the machinery behind the unique behaviours of the two-dimensional plasmonic waves and discusses how they can be engineered to create ultra-subwavelength plasmonic circuits and metamaterials for infrared and gigahertz to terahertz integrated electronics.

Individual electrons in graphene behave as massless quasiparticles. Unexpectedly, it is inferred from plasmonic investigations that electrons in graphene must exhibit a non-zero mass when collectively excited. The inertial acceleration of the electron collective mass is essential to explain the behaviour of plasmons in this material, and may be directly measured by accelerating it with a time-varying voltage and quantifying the phase delay of the resulting current. This voltage-current phase relation would manifest as a kinetic inductance, representing the reluctance of the collective mass to accelerate. However, at optical (infrared) frequencies, phase measurements of current are generally difficult, and, at microwave frequencies, the inertial phase delay has been buried under electron scattering. Therefore, to date, the collective mass in graphene has defied unequivocal measurement. Here, we directly and precisely measure the kinetic inductance, and therefore the collective mass, by combining device engineering that reduces electron scattering and sensitive microwave phase measurements. Specifically, the encapsulation of graphene between hexagonal boron nitride layers, one-dimensional edge contacts and a proximate top gate configured as microwave ground together enable the inertial phase delay to be resolved from the electron scattering. Beside its fundamental importance, the kinetic inductance is found to be orders of magnitude larger than the magnetic inductance, which may be utilized to miniaturize radiofrequency integrated circuits. Moreover, its bias dependency heralds a solid-state voltage-controlled inductor to complement the prevalent voltage-controlled capacitor.

We have developed a miniature nuclear magnetic resonance (NMR) system. By combining the physics of NMR with CMOS radio-frequency ICs, we developed a 0.1-kg palm NMR system that is 1,200 times smaller, 1,200 times lighter, and yet 150 times more spin-mass sensitive than a state-of-the-art 120-kg commercial benchtop system. The small NMR system can be used for disease detection and medical diagnostics. It was demonstrated capable of detecting human cancer cells and cancer marker proteins.

Solid-state electronic devices can be engineered to detect and manipulate biological molecules and cells by using electric or magnetic interactions. The integrated circuits, which can contain a large number of such devices, may then potentially be developed into low-cost chip-scale platforms to perform bioanalytical tasks in a multiplexed manner for applications in biology, biotechnology, and personalized medicine. This paper reviews some recent developments in this solid-state electronic and biological systems interface.

We report an 11-b 20-Ms/s pipelined ADC in 0.18-μm CMOS with a novel dual-mode-based digital background calibration method that altogether corrects errors caused by gain insufficiency, gain nonlinearity, and capacitor mismatches. The calibration enables an intentional use of low-gain single-stage op amps instead of conventional high-gain multi-stage op amps, with which we achieve a total ADC power dissipation of 2.9 mW and a short convergence time of 105. The calibration improves the SNDR from 45 dB to 60 dB, and the SFDR from 50 dB to 86 dB. The figure-of-merit is 174 fJ/conversion-step.

We report electronics regime (GHz) two-dimensional (2D) plasmonic circuits, which locally and nonresonantly interface with electronics, and thus offer to electronics the benefits of their ultrasubwavelength confinement, with up to 440,000-fold mode-area reduction. By shaping the geometry of 2D plasmonic media 80 nm beneath an unpatterned metallic gate, plasmons are routed freely into various types of reflections and interferences, leading to a range of plasmonic circuits, e.g., plasmonic crystals and plasmonic-electromagnetic interferometers, offering new avenues for electronics.

Metamaterials with negative refractive indices can manipulate electromagnetic waves in unusual ways, and can be used to achieve, for example, sub-diffraction-limit focusing, the bending of light in the 'wrong' direction, and reversed Doppler and Cerenkov effects. These counterintuitive and technologically useful behaviours have spurred considerable efforts to synthesize a broad array of negative-index metamaterials with engineered electric, magnetic or optical properties. Here we demonstrate another route to negative refraction by exploiting the inertia of electrons in semiconductor two-dimensional electron gases, collectively accelerated by electromagnetic waves according to Newton's second law of motion, where this acceleration effect manifests as kinetic inductance. Using kinetic inductance to attain negative refraction was theoretically proposed for three-dimensional metallic nanoparticles and seen experimentally with surface plasmons on the surface of a three-dimensional metal. The two-dimensional electron gas that we use at cryogenic temperatures has a larger kinetic inductance than three-dimensional metals, leading to extraordinarily strong negative refraction at gigahertz frequencies, with an index as large as -700. This pronounced negative refractive index and the corresponding reduction in the effective wavelength opens a path to miniaturization in the science and technology of negative refraction.

We report a mode-locked electrical oscillator fully integrated in GaAs. It self generates a periodic train of pulses with a 16-ps pulse width and a 18.7-GHz frequency. This is the fastest electrical mode-locked oscillator to date, and the first integration of reflective mode-locked electrical oscillator. It works by sending a pulse back and forth on a coplanar waveguide with reflections at both ends. The reflection occurs with level-dependent gain that enables pulse formation and stabilization.

This paper describes a new method for fabricating highly stretchable and robust electrical circuits. The circuits consist of liquid metal (eutectic gallium indium alloy, EGaIn) enclosed in elastomeric microfluidic channels. In particular, a microfluidic hybrid structure made of two types of elastomers (polydimethylsiloxane (PDMS) and Ecoflex (type 0030, Reynolds Advanced Materials) with different stiffness has been developed to improve the stretchability and mechanical stability of the circuits. These circuits can be flexed, twisted, and stretched up to 2.2 times of their original length l 0 . When we applied this stretchable circuit for radio-frequency antennas, the antennas exhibited no degradation in reflected power even after being repeatedly stretched to l = 1.50 l 0 more than 100 times. This stretchability also allows the resonance frequencies of the antennas to be mechanically tuned around 1 GHz. The stretchable and robust circuits may be useful in reconfigurable and conformal structures, wearable sensors and large-area electronics, and other devices that must undergo large mechanical deformation.

This paper reviews our first miniature nuclear magnetic resonance (NMR) system originally reported in [1], [2], which, weighing only 2 kg, is 60 times lighter, 40 times smaller, yet 60 times more spin mass sensitive than a 120-kg state-of-the-art commercial benchtop NMR system. The miniaturization was made possible by combining the physics of NMR with a high-performance CMOS radio-frequency integrated circuit. The system is aimed at sensing biomolecules such as cancer marker proteins, and represents a circuit designer's approach to pursue low-cost diagnostics in a portable platform. Our most recent development of even smaller NMR systems [3] will not be reviewed here, as it has yet to be exposed in full through a journal publication first.