CMOS Electronics Research Articles

(Invited) Continuous Monitoring of Small Molecules Using Electrochemical Aptamer-Based Biosensors with CMOS Electronics

The ability to continuously monitor specific “molecules” over a long period of time can provide fundamentally new insights into disease dynamics and the transition from a healthy state and lead to the design of next-generation screening and detection tools. However, currently only a few biomolecules, such as glucose, oxygen, and dopamine, can be continuously and real-time monitored with significant relevance to chronic disease management. The prevalent glucose sensor uses glucose oxidase (GOx), an enzyme designed to oxidize glucose persistently in its proximity, producing an electrochemical current proportional to the glucose concentration. The enzyme's specificity means it cannot be readily adapted to target different biomolecules, thus constraining its versatility. This limitation also extends to many enzyme-based sweat sensors. In contrast, oxygen and dopamine measurements exploit their inherent molecular characteristics. Oxygen saturation (SpO2) in blood is determined via pulse oximetry, which uses the distinct light absorption properties of deoxygenated and oxygenated blood under red and infrared lights. Dopamine, a neurotransmitter integral to our emotional responses, is highly electrochemically active and can undergo reversible oxidation, allowing it to be detected by analytical methods like fast-scan cyclic voltammetry (FSCV). Nevertheless, such distinct properties are not common among biomolecules, making these methods non-transferable to a broader range.To this end, our group and others have previously utilized aptamers to achieve continuous detection of small molecules in vivo. Aptamers are “synthetic antibodies” composed of nucleic acids that can specifically bind to the target analytes in complex samples, such as the whole blood (Fig. 1(a)). Importantly, they can be engineered into “aptamer-switches” that undergo structure-switching upon target binding in a reversible manner. By conjugating electroactive reporters to the aptamers, the changes in their structure (thus, the analyte concentration) can be detected electrochemically. As sample preparation is not needed, aptamer switches are capable of continuous monitoring of biomolecules in vivo.Coupling with structure-switching aptamers, our team has presented the first wireless, electrochemical aptamer-sensing chip in the 65-nm CMOS technology and achieved continuous recording of small-molecule drugs, e.g., antibiotics or chemotherapeutics, from a freely moving rodent (Fig. 1(b) and 1(c)). The chip features a chronoamperometric (CA) sensing circuit that probes the electron transfer (ET) kinetics of the structure-switching aptamers that are correlated to the concentration of target analytes. Notably, we have innovated a sample-and-hold (S/H) circuit technique into our readout front end to overcome the noise/power trade-off commonly experienced in conventional circuit design (Fig. 1(d)). This technique employs two switched-capacitor circuits that maintain the electrode potentials on an open-loop basis, disabling the power-intensive and noise-contributing on-chip amplifiers during the recording phase. The technique achieves simultaneous reductions of 286× in circuit noise (4.36 nArms to 15.2pArms) and 23× in power consumption (5.25 mW to 0.22 mW), along with a 10× increase in throughput compared to the traditional square-wave voltammetry (SWV) readout methods that have been commonly used in interrogating E-AB sensors (5 vs. 0.5 Samples/sec). Fig. 1(d) shows the measured current transients that reflects the changes in ET kinetics at different target concentrations.While previous circuit focuses on lowering the electronics noise, we also develop a second electrochemical readout circuit that aims at boosting the detection signal through redox current integration at the circuit domain. This integration process captures the charges, instead of the current, leading us to term this technique square-wave voltcoulometry (SWVC, Fig. 1(e)). Our analysis demonstrates that the proposed SWVC technique can yield a remarkable signal improvement of 250×. Importantly, this improvement is achieved while maintaining nearly identical levels of input-referred noise (5 pArms) at a power consumption of only few mW. Fig. 1(f) compares the measurements obtained using conventional SWV readout and the proposed SWVC technique. The results demonstrate a remarkable 25-fold improvement in the signal-to-noise ratio (SNR), and we anticipate another 4× boosting once we optimize the test setup.We've also addressed issues related to drift and biofouling. We utilize kinetic-differential measurements (KDM) that monitor the rate of current change rather than absolute current values, mitigating the effects of biosensor detachment from the electrode surface. We also develop a dual-aptamer strategy where two aptamer sensors responding differentially to the same analyte targets are utilized to increase the signal while rejecting the slow-moving drifts (Fig. 1(g)). For biofouling, we employ a combinatorial-selected polyacrylamide hydrogel coating to specifically resist platelet adhesion (Fig. 1(h)). By integrating these advancements, we have validated our technology in vivo within whole blood via a probe catheterized into a rat's vein and interstitial fluids (ISF) through whole-system implantation (Fig. 1(i)). This technology also holds promise for the multiplexed monitoring. Figure 1

All-2D-Materials Subthreshold-Free Field-Effect Transistor with Near-Ideal Switching Slope.

The Boltzmann Tyranny, set by thermionic statistics, dictates the lower limit of switching slope (SS) of a MOSFET to be 60 mV/dec, the fundamental barrier for low-dissipative electronics. The large SS leads to nonscalable voltage, significant leakage, and power consumption, particularly at short channels, making transistor scaling an intimidating challenge. In recent decades, an array of steep-slope transistors has been proposed; none is close to an ideal switch with ultimately abrupt switching (SS ∼ 0 mV/dec) between the binary logic states. We demonstrated an all-2D-materials van-der-Waals-heterostructure (vdW)-based FET that exhibits ultrasteep switching (0.33 mV/dec), a large on/off current ratio (∼107), and an ultralow off current (∼0.1 pA). The "Subthreshold-Free" operation achieved by the collective behavior of functional materials enables FET switching directly from the OFF-state to the ON-state with entirely eliminated subthreshold region, behaving as the ideal logic switch. Two-inch wafer-scale device fabrication is demonstrated. Boosted by device innovation and emerging materials, the research presents an advancement in achieving the "beyond-Boltzmann" transistors, overcoming one of the CMOS electronics' most infamous technology barriers that have plagued the research community for decades.

Nanophotonic phased array XY Hamiltonian solver

Solving large-scale computationally hard optimization problems using existing computers has hit a bottleneck. A promising alternative approach uses physics-based phenomena to naturally solve optimization problems, wherein the physical phenomena evolve to their minimum energy. In this regard, photonics devices have shown promise as alternative optimization architectures, benefiting from high-speed, high-bandwidth, and parallelism in the optical domain. Among photonic devices, programmable spatial light modulators (SLMs) have shown promise in solving large scale Ising model problems, to which many computationally hard problems can be mapped. Despite much progress, existing SLMs for solving the Ising model and similar problems suffer from slow update rates and physical bulkiness. Here, we show that using a compact silicon photonic integrated circuit optical phased array (PIC-OPA), we can simulate an XY Hamiltonian, a generalized form of the Ising Hamiltonian, where spins can vary continuously. In this nanophotonic XY Hamiltonian solver, the spins are implemented using analog phase shifters in the optical phased array. The far field intensity pattern of the PIC-OPA represents an all-to-all coupled XY Hamiltonian energy and can be optimized with the tunable phase-shifters, allowing us to solve an all-to-all coupled XY model. Our results show the utility of PIC-OPAs as compact, low power, and high-speed solvers for nondeterministic polynomial-hard problems. The scalability of the silicon PIC-OPA and its compatibility with monolithic integration with CMOS electronics further promise the realization of a powerful hybrid photonic/electronic non-Von Neumann compute engine.

High-density superconductive logic circuits utilizing 0 and π josephson junctions

Superconductor Electronics (SCE) is a fast and power-efficient technology with great potential for overcoming conventional CMOS electronics’ scaling limits. Nevertheless, the primary challenge confronting SCE today is its integration level, which lags several orders of magnitude behind CMOS circuits. In this study, we have innovated and simulated a novel logic family grounded in the principles of phase shifts occurring in 0 and π Josephson junctions. The fast phase logic (FPL) eliminates the need for large inductor loops and shunt resistances by combining the half-flux and phase logic. Therefore, the Josephson junction (JJ) area only limits the integration density. The cells designed with this paradigm are fast, and the clock-to-Q delay for logic cells is about 4ps. While maintaining over 50% parameter margins for wiring cells. This logic is power efficient and can increase the integration by at least 100×in the SCE chips.

Extended Lifetime Testing of SiC CMOS Electronics at 500°C

Silicon Carbide (SiC) CMOS electronics is a promising approach for realizing high level of integration, especially for implementing digital functions, while significantly reducing the power dissipation on chip compared to NMOS-only, or JFET approaches. Gate oxide in MOSFET-based electronics pose a potential reliability challenge for operating at extreme temperatures. GE has previously developed gate oxide reliability models that predicted reliable operation at 500°C, but experimental validation had not been conducted previously. Recent testing results of testing of 500°C operation of SiC CMOS based integrated circuit over 60 days of continuous operation are presented. The results show the gate oxide surviving extended operating time of both NMOS and PMOS devices at 500°C. and thereby enabling a roadmap towards realizing more complex digital function at extreme temperature >=500°C.

Junction temperature of CMOS electronics cooled by a Stirling cryocooler

This case study addresses the practical challenges associated with operating cryo-CMOS electronics. Previous research has been largely confined to impractical liquid cryogen cooling and the few under-reported examples of implementing electric cryocoolers. This study further clarifies the operation of cryo-CMOS devices cooled by electric cryocoolers. It develops and experimentally validates an analytical relation between the junction temperature and the parameters of a cryogenic system. To validate this relationship, we placed a printed circuit board in a thermal chamber, cooled it to 173 K using a Stirling cryocooler, and varied input clock frequencies. The measured values of the junction temperature were compared with calculations, which showed good prediction accuracy with a coefficient of variance of ±2%, a mean biased error of −2%, and a determination coefficient of 0.92. In addition, the measurements provided evidence for a multi-fold increase in the clock frequency of cryo-CMOS electronics. The results of this study help estimate accurately the steady-state junction temperature of cryo-CMOS devices in a wide range of cryogenic temperatures for different types of cryocoolers.

BLAST: A Wafer‐Scale Transfer Process for Heterogeneous Integration of Optics and Electronics

AbstractA general transfer method is presented for the heterogeneous integration of different photonic and electronic materials systems and devices into a single substrate. Called BLAST, for Bond, Lift, Align, and Slide Transfer, the process works at wafer scale and offers precision alignment, high yield, varying topographies, and suitability for subsequent lithographic processing. BLAST's capabilities is demonstrated by integrating both GaAs and GaN µLEDs with silicon photovoltaics to fabricate optical wireless integrated circuits that up‐convert photons from the red to the blue. The study also shows that BLAST can be applied to a variety of other devices and substrates, including CMOS electronics, vertical cavity surface emitting lasers (VCSELs), and 2D materials. BLAST further enables the modularization of optoelectronic microsystems, where optical devices fabricated on one material substrate can be lithographically integrated with electronic devices on a different substrate in a scalable process.

An accurate circuit model of Ge/Si single photon avalanche diode

Ge/Si single-photon avalanche diodes (SPADs) have benefits of low after-pulsing probability, low-cost and compatibility with CMOS electronics compared to InGaAs/InP counterpart, thus presenting great potentials for imaging and optical quantum applications in short-wave infrared (SWIR). In this work, an equivalent circuit model mimicking the behavior of pseudo-planar Ge/Si SPAD is constructed to provide accurate electronic information for the co-design of front-end circuit. The DC properties are modelled by nonlinear resistors, voltage-controlled switches and voltage sources, and the AC characteristics are emulated by junction and stray capacitances. To accurately evaluate the statistical behavior, thermal excitation and trap-assisted tunneling are incorporated in the built SPAD circuit models, where three-level traps are adopted to effectively fit the after-pulsing probability. The key model parameters such as electric field profile, breakdown voltage and avalanche triggering probability, are extracted from 2D device simulation. The developed Ge/Si SPAD circuit model implemented in Verilog-A hardware description language (HDL) with a gated passive quenching/reset architecture is validated by circuit simulation platform. The simulation results are in good agreement with the previously reported measurement data, demonstrating the effectiveness and accuracy of our Ge/Si SPAD circuit model.

Time‐Multiplexed Control of Programmable Silicon Photonic Circuits Enabled by Monolithic CMOS Electronics

AbstractProgrammable photonic circuits require an electronic control layer to configure and stabilize the optical functionality at run‐time. Such control action is normally implemented by supervising the status of the circuit with integrated light monitors and by providing feedback signals to integrated actuators. This paper demonstrates that the control action can be effectively performed with electrical signals that are time‐multiplexed directly on the photonic chip. To this aim, the necessary electronic functionalities are monolithically integrated in a conventional 220 nm silicon photonics platform with no changes to the standard fabrication process. By exploiting a non‐conventional structure to implement metal‐oxide–semiconductor field‐effect transistors, an electronic controller is co‐designed into a programmable photonic circuit to enable a time‐multiplexed readout of integrated photodetectors and sequential activation of thermal phase shifters with on‐chip electronic memory. The accuracy of the time‐multiplexed control, achieved on a time scale of less than 10 ms, is demonstrated by penalty‐free routing of 10 Gbit s−1 modulated signals. This approach can be straightforwardly applied to large‐scale photonic chips to reduce the number of required electrical input/output connections.

Graphene-Based Optoelectronic Mixer Device for Time-of-Flight Distance Measurements for Enhanced 3D Imaging Applications.

A large and growing number of applications benefit from innovative and powerful 3D image sensors. Graphene photodetectors can achieve 3D sensing functionalities by intrinsic optoelectronic frequency mixing due to the nonlinear output characteristics of the sensor. In first proof of principle distance measurement demonstrations, we achieve modulation frequencies of 3.1 MHz, signal-to-noise ratios of ∼40 dB, distance detection up to at least 1 m, and a mean accuracy of 25.6 mm. The scalable More than Moore detector approach enables geometrical fill factors close to 100% and can easily complement powerful functionalities by simple back-end integration on top of CMOS electronics.

500 MHz high resolution proximity sensors with fully integrated digital counter

We report on the design and characterization of two inductive proximity sensors based on LC oscillators operating at 500 MHz. The distance from the target is obtained by measuring the oscillation frequency variation. Both sensors contain an off-chip LC resonator consisting of a two turns 4 mm diameter planar coil and a ceramic capacitor. The LC resonator is connected to integrated CMOS electronics. The first sensor output stage consists of a buffer whereas the second sensor output stage includes a co-integrated 21 bits digital frequency counter. The first sensor has frequency noise floor of 0.085 Hz/Hz above 3 kHz. At a distance of 200 μm from the coil, the resolution is 0.2 pm/Hz and the integrated resolution from 1 mHz to 1 kHz is 22 pmrms. The second sensor reaches a noise floor of 2 Hz/Hz corresponding to a resolution of 5 pm/Hz and an integrated resolution of 900 pmrms.

Microfabricated albedo insensitive sun position sensor system in silicon carbide with integrated 3D optics and CMOS electronics

Microfabricated albedo insensitive sun position sensor system in silicon carbide with integrated 3D optics and CMOS electronics

Timing resolution in double-sided silicon photon-counting computed tomography detectors.

Our purpose is to investigate the timing resolution in edge-on silicon strip detectors for photon-counting spectral computed tomography. Today, the timing for detection of individual x-rays is not measured, but in the future, timing information can be valuable to accurately reconstruct the interactions caused by each primary photon. We assume a pixel size of and a detector with double-sided readout with low-noise CMOS electronics for pulse processing for every pixel on each side. Due to the electrode width in relation to the wafer thickness, the induced current signals are largely dominated by charge movement close to the collecting electrodes. By employing double-sided readout electrodes, at least two signals are generated for each interaction. By comparing the timing of the induced current pulses, the time of the interaction can be determined and used to identify interactions that originate from the same incident photon. Using a Monte Carlo simulation of photon interactions in combination with a charge transport model, we evaluate the performance of estimating the time of the interaction for different interaction positions. Our simulations indicate that a time resolution of 1ns can be achieved with a noise level of 0.5keV. In a detector with no electronic noise, the corresponding time resolution is . Time resolution in edge-on silicon strip CT detectors can potentially be used to increase the signal-to-noise-ratio and energy resolution by helping in identifying Compton scattered photons in the detector.

Coherent LiDAR With an 8,192-Element Optical Phased Array and Driving Laser

We present recent advancements of optical phased array LiDAR with record-performance system demonstrations. First, we give an overview of the technology and how it combines the benefits of coherent LiDAR with the integration capabilities of silicon photonics. Then, an 8192-element optical phased array is shown with individually-addressed elements driven by custom CMOS electronics. This compact chip-scale beam-steering engine is enabled by flip-chip attached ASICs on the photonic integrated circuit. The optical phase shifters and emitters in the array have a 1 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mu$</tex-math></inline-formula> m pitch to enable a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$100^{\circ }\times 17^\circ$</tex-math></inline-formula> field of view. This unprecedented number of active elements forms a near centimeter-scale aperture. Next, a high-performance laser uniquely suited for optical phased array LiDAR is demonstrated. Due to the silicon photonics cavity, it simultaneously supports a large tuning range (60 nm), low linewidth ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\sim$</tex-math></inline-formula> 50 kHz), and fast linear chirp (1.3 GHz in 17.5 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mu$</tex-math></inline-formula> s). Finally, a solid-state coherent LiDAR system is realized with transmit/receive optical phased arrays coupled to an on-chip coherent receiver while being driven by the demonstrated laser. Ranging is shown on diffusive targets while simultaneously extracting velocity at each point in the point cloud. To the best of our knowledge, this single-unit compact system represents the state-of-the-art in optical phased array LiDAR technology.

(Invited) Nanoelectronics Based on Assembled High-Density and High-Semiconducting-Purity Carbon Nanotube Films

Carbon nanotubes hold great promise for high-performance electronics but also face significant challenges in terms of assembly and integration. On one hand, aligned carbon nanotubes are proposed as an alternative to III-V semiconductor technologies in radio frequency (RF) applications because of their high linearity as amplifiers and compatibility with CMOS electronics. We will first report high-performance RF transistors with operation frequencies beyond 100 GHz. These devices are built upon high-density (~50 nanotubes / micron) and high semiconducting purity (> 99.99%) aligned single-wall carbon nanotube films assembled at wafer scale. With gate length ~110 nm and T-shaped gate to reduce the gate charging resistance, the devices showed an extrinsic cutoff frequency and maximum oscillation frequency of over 100 GHz. The performance surpasses the 90 GHz cutoff frequency of radio-frequency CMOS transistors with gate length of 100 nm and is close to the performance of GaAs technology. [1] On the other hand, Carbon nanotubes are ideal candidates for beyond-silicon nanoelectronics because of their high mobility and low-cost processing; however, n-type transistors based on assembled aligned nanotubes has not been reported yet. Fabrication of n-type behavior field effect transistors (FETs) based on assembled aligned CNT arrays is needed for advanced CNT electronics. We will report a scalable process to make n-type transistors based on assembled aligned CNT arrays. Air-stable and high-performance n-type CNT FETs are achieved with high yield by combining atomic layer deposition dielectric and Ti contacts with gold overcoating, which are stable in air and widely used for III-V semiconductors. We also systematically studied the contribution of metal contacts and atomic layer deposition passivation in determining the transistor polarity. [2] Based on these experimental results, we report the successful demonstration of complementary metal-oxide-semiconductor inverters with good performance, which paves the way to realizing the promising future of carbon nanotube nanoelectronics.[1] “Wafer-scalable, aligned carbon nanotube transistors operating at frequencies of over 100 GHz”, C. Rutherglen, A. A. Kane, P. F. Marsh, T. A. Cain, B. I. Hassan, M. R. AlShareef, C. Zhou and K. Galatsis, Nature Electronics, volume 2, pages 530–539, 2019.[2] “Air-Stable n-Type Transistors based on Assembled Aligned Carbon Nanotube Arrays and Their Application in CMOS Electronics”, Z. Li, K. R. Jinkins, D. Cui, M. Chen, Z. Zhao, M. S. Arnold and C. Zhou, Nano Res. (2021). https://doi.org/10.1007/s12274-021-3567-9.

Optical Sensing of Chlorophyll(in) With Dual-Spectrum Si LEDs in SOI-CMOS Technology

Small and low-cost chlorophyll sensors are popular in agricultural sector and food-quality control.Combining such sensors with silicon CMOS electronics is challenged by the absence of silicon-integrated light-sources.We experimentally achieve optical absorption sensing of chlorophyll based pigments with silicon (Si) micro light-emitting diodes (LED) as light-source, fabricated in a standard SOI-CMOS technology.By driving a Si LED in both forward and avalanche modes of operation,we steer its electroluminescentspectrum between visible (400–900 nm) and near-infrared (~1120 nm). For detection of chlorophyll in solution phase, the dualspectrum light from the LED propagates vertically through glycerol micro-droplets containing sodium copper chlorophyllin at varying relative concentrations. The transmitted light is detected via an off-chip Si photodiode. The visible to near-infrared color ratio (COR) of the photocurrent yields the effective absorption coefficient. We introduce the LED-specificmolar absorption coefficient as ametric to compute the absolute pigment concentration (~0.019 ± 0.006 mol L <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−1</sup> ) and validate the results by measurements with a hybrid spectrophotometer. With the same sensor, we also show noninvasive monitoring of chlorophyll in plant leaves. COR sensitivities <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\sim 3.9 \times 10^{4}$ </tex-math></inline-formula> mol <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−1</sup> L and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\sim 5.3 \times 10^{4}$ </tex-math></inline-formula> mol <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−1</sup> L are obtained for two leaf species, where light from the LED propagates diffusely through the thickness of the leaf prior to detection by the photodiode. Our work demonstrates the feasibility of realizing fully CMOS-integrated optical sensors for biochemical analyses in food sector and plant/human health.

Electronically Reconfigurable Photonic Switches Incorporating Plasmonic Structures and Phase Change Materials.

The ever‐increasing demands for data processing and storage will require seamless monolithic co‐integration of electronics and photonics. Phase‐change materials are uniquely suited to fulfill this function due to their dual electro‐optical sensitivity, nonvolatile retention properties, and fast switching dynamics. The extreme size disparity however between CMOS electronics and dielectric photonics inhibits the realization of efficient and compact electrically driven photonic switches, logic and routing elements. Here, the authors achieve an important milestone in harmonizing the two domains by demonstrating an electrically reconfigurable, ultra‐compact and nonvolatile memory that is optically accessible. The platform relies on localized heat, generated within a plasmonic structure; this uniquely allows for both optical and electrical readout signals to be interlocked with the material state of the PCM while still ensuring that the writing operation is electrically decoupled. Importantly, by miniaturization and effective thermal engineering, the authors achieve unprecedented energy efficiency, opening up a path towards low‐energy optoelectronic hardware for neuromorphic and in‐memory computing.

Broadband Meandered Thin-Film Lithium Niobate Modulator With Ultra-Low Half-Wave Voltage

Compact thin-film lithium niobate (TFLN) modulators with low half-wave voltage <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{V}_{\pi }$ </tex-math></inline-formula> are highly desirable for many applications. In particular, modulators with <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{V}_{\pi }~\sim ~1$ </tex-math></inline-formula> V would allow direct driving by CMOS circuits, but they normally require a long modulation length of several centimeters. Folded TFLN modulators exhibit reduced <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{V}_{\pi }$ </tex-math></inline-formula> together with a small device footprint. However, previously reported schemes suffer from complicated device fabrication procedure to maintain the relative direction of electric field with respect to the TFLN crystal polarization after electrode folding. In this work, a meandered X-cut TFLN Mach–Zehnder (MZ) modulator with specially designed capacitively-loaded traveling-wave electrodes (CL-TWEs) is demonstrated. Interdigitated T-rails are employed to reverse the electric field in the folded region for continuous accumulation of optical phase shift. Ultra-low <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{V}_{\pi }$ </tex-math></inline-formula> of 1.08 V is achieved on an 8-mm-long modulator containing three-segments of 7-mm-long modulation sections, together with a 3-dB electro-optic bandwidth around 43 GHz. The broadband meandered modulator with ultra-low half-wave voltage as well as a compact footprint has the potential to be directly driven by CMOS electronics.

A Compact 112-Gbaud PAM-4 Silicon Photonics Transceiver for Short-Reach Interconnects

For next generation highly integrated transceivers, silicon photonics (SiP) has attracted widespread interest in using mature CMOS production processes to manufacture high-yield, low-cost photonic integrated circuits (PIC) with the potential for integration with CMOS electronics. SiP now routinely integrate GeSi electroabsorption modulators (EAM) and GeSi waveguide photodiodes which have high responsivity and possess 3-dB electro-optic bandwidth of over 65 GHz. Their ultra-compact dimensions make it possible for multi-channel transceivers to be realized on a small chip area. In this paper, we demonstrate the high-speed capability of these devices incorporated with optimized digital signal processing (DSP) for 100 Gbaud+ PAM-4 signaling. Using integrated GeSi-EAM and GeSi-photodiode fabricated at a commercial foundry, we carried out intensity modulation and direct detection (IM-DD) transmission experiments in C-band using PAM-4, for both back-to-back and SSMF transmission at 1 km and 1.5 km. Under a 6-dB system bandwidth of ∼43GHz we attained, with the help of DSP equalization, a record 112 Gbaud (224 Gb/s), 108 Gbaud (216 Gb/s) and 100 Gbaud (200 Gb/s) are achieved over back-to-back, 1 km and 1.5 km SSMF transmission respectively, with a bit-error-rate (BER) below the hard-decision forward-error-correction (HD-FEC) threshold of 3.8E-3.

Organic–Inorganic Hybrid Interfaces for Spin Injection into Carbon Nanotubes and Graphene

AbstractSpintronics is a quantum technology which aims at adding the spin quantum degree of freedom to conventional CMOS electronics. Since the discovery of the giant magneto‐resistance in 1988, considered as the birth of this field, spintronics continues flooding the market with plethora of devices used in everyday life applications such as hard drive read heads or magnetic random‐access memories, and so on. From a fundamental research perspective, the field is still blooming bringing post‐CMOS perspectives technologically closer to the reality with, for instance, prototypes of all‐spin‐logic circuits and neuromorphic chips. To sustain this intense research activity, a quest for new platform materials is also taking place not only to enhance existing performances but also to generate novel functionalities. In this vein, carbon nanostructures such as molecules, graphene, and carbon nanotubes are among the most sought‐after materials. In this review, spin transport experiments in carbon nanotubes and graphene are first detailed and then, the necessity to consider new hybrid interfaces are highlighted for a better control of the spin injection at the quantum device level.