Large Scale Integration Devices Research Articles

(Invited) Energy Intelligent Computing Devices Based on 2D Materials

Despite the long and crucial role of traditional solid-state physics for current silicon-based technologies, next generation neuromorphic, non-volatile memory, and energy devices that are key components in the era of the internet of things (IOT) require novel working principles with quantum physics emerging in low-dimensional materials1-4. The main research direction for the future devices is to realize ‘ultralow device operation energy’, ‘ultrahigh device operation speed’, and ‘large-scale device integration (up to 1015)’, which calls for exploring diverse quantum phenomena in low dimensional device components5,6. In this talk, I will present some of our recent efforts1-7 to establish new device physics for energy intelligent devices, which could be a milestone for the promising future devices. In particular, dynamic convolution neural network, phase transition and other intriguing quantum physics in two-dimensional (2D) materials will be discussed along with logic device, neuromorphic computing, and energy device applications. Reference H. Yang et al. Graphene Barristor, a Triode Device with a Gate-Controlled Schottky Barrier, Science 336, 1140 (2012)S. Cho et al. Phase Patterning for Ohmic Homojunction Contact in MoTe2. Science 349, 625 (2015)D. H. Keum et al. Bandgap opening in few-layered monoclinic MoTe2. Nature Physics 11, 482 (2015)H. Yang et al. Structural and quantum-state phase transition in van der Waals layered materials. Nature Physics 13, 931 (2017)L. Sun et al. Self-selective van der Waals heterostructures for large-scale memory array. Nature Communications 10, 3161 (2019)S. Zheng et al. Resonant tunneling spectroscopy to probe the giant Stark effect in atomically-thin materials. Advanced Materials 32, 1906942 (2020)L. Sun et al. In-sensor Reservoir Computing for Language Learning via Two-dimensional Memristor. Science Advances 7, eabg1455 (2021)

Self-Competitive Growth of CsPbBr3 Planar Nanowire Array.

Semiconductor planar nanowire arrays (PNAs) are essential for achieving large-scale device integration. Direct heteroepitaxy of PNAs on a flat substrate is constrained by the mismatch in crystalline symmetry and lattice parameters between the substrate and epitaxial nanowires. This study presents a novel approach termed "self-competitive growth" for heteroepitaxy of CsPbBr3 PNAs on mica. The key to inducing the self-competitive growth of CsPbBr3 PNAs on mica involves restricting the nucleation of CsPbBr3 nanowires in a high-adsorption region, which is accomplished by overlaying graphite sheets on the mica surface. Theoretical calculations and experimental results demonstrate that CsPbBr3 nanowires oriented perpendicular to the boundary of the high-adsorption area exhibit greater competitiveness in intercepting the growth of nanowires in the other two directions, resulting in PNAs with a consistent orientation. Moreover, these PNAs exhibit low-threshold and stable amplified spontaneous emission under one-, two-, and three-photon excitation, indicating their potential for an integrated laser array.

High performance, single crystal gold bowtie nanoantennas fabricated via epitaxial electroless deposition

Material quality plays a critical role in the performance of nanometer-scale plasmonic structures and represents a significant hurdle to large-scale device integration. Progress has been hindered by the challenges of realizing scalable, high quality, ultrasmooth metal deposition strategies, and by the poor pattern transfer and device fabrication yields characteristic of most metal deposition approaches which yield polycrystalline metal structure. Here we highlight a novel and scalable electrochemical method to deposit ultrasmooth, single-crystal (100) gold and to fabricate a series of bowtie nanoantennas through subtractive nanopatterning. We investigate some of the less well-explored design and performance characteristics of these single-crystal nanoantennas in relation to their polycrystalline counterparts, including pattern transfer and device yield, polarization response, gap-field magnitude, and the ability to model accurately the antenna local field response. Our results underscore the performance advantages of single-crystal nanoscale plasmonic materials and provide insight into their use for large-scale manufacturing of plasmon-based devices. We anticipate that this approach will be broadly useful in applications where local near-fields can enhance light–matter interactions, including for the fabrication of optical sensors, photocatalytic structures, hot carrier-based devices, and nanostructured noble metal architectures targeting nano-attophysics.

Strain-induced ordered Ge(Si) hut wires on patterned Si (001) substrates.

Ge/Si nanowires are predicted to be a promising platform for spin and even topological qubits. While for large-scale integration of these devices, nanowires with fully controlled positions and arrangements are a prerequisite. Here, we have reported ordered Ge hut wires by multilayer heteroepitaxy on patterned Si (001) substrates. Self-assembled GeSi hut wire arrays are orderly grown inside patterned trenches with post growth surface flatness. Such embedded GeSi wires induce tensile strain on the Si surface, which results in preferential nucleation of Ge nanostructures. Ordered Ge nano-dashes, disconnected wires and continuous wires are obtained correspondingly by tuning the growth conditions. These site-controlled Ge nanowires on a flattened surface lead to the ease of fabrication and large-scale integration of nanowire quantum devices.

Nanopatterning Technologies of 2D Materials for Integrated Electronic and Optoelectronic Devices (Adv. Mater. 52/2022)

Nanopatterning Nanopatterning bridges the microstructure of 2D materials and the integrated chip devices, essentially enabling and prompting their successful industrial application. In article number 2200734, Yuan Li, Tianyou Zhai, and co-workers review the recent development of key nanopatterning technologies for 2D materials with the aim of realizing their large-scale device integration. The contribution offers pioneering reference and guidelines to promote 2D materials from laboratory research to practical use.

ALD-Based Synthesis of Wafer-Scale Transition Metal Dichalcogenides Towards Nanoelectronics and Optoelectronics Applications

Two-dimensional (2D) transition metal dichalcogenides (TMDs), such as MoS2 and WS2 have been widely studied due to their unique physical and electronic properties even at one atomic layer thickness. Since the first report on the MoS2 field-effect transistor (FET) device [1], great efforts have been made in the past decade to extend the intriguing features of TMDs to practical applications. However, such integration has been severely bottlenecked by the lack of effective approaches to achieve wafer-scale, uniform, crystalline and stoichiometric TMD films.Till now, it is still prevalent to fabricate TMD-based electronic devices using mechanical exfoliation methods. Although single-crystal flakes with least defects can be obtained, the size, thickness and location of the exfoliated TMD flakes are largely uncontrollable, making it unsuitable for large-scale device integration and massive production. So far, various synthetic approaches have been proposed to grow large-area TMD thin films. Chemical vapor deposition (CVD)-based method is one of the major routines to synthesize high-quality monolayer and few-layer TMD flakes [2-4]. For example, in typical CVD processes to grow MoS2, the films can be achieved either by the reduction reaction between the S and MoO3 source powders or by sulfurizing the Mo (or MoOx) films pre-deposited by using physical vapor deposition. However, the nucleation sites in the CVD process are uncontrollable which may lead to the vertical stacking of the MoS2 flakes in triangle shape deteriorating the crystalline properties of the film. On the other hand, the pre-deposited Mo or MoOx film by using e-beam evaporation or sputtering usually suffer from rough surface morphology and unsatisfactory film uniformity which further limit the homogeneity of the large-scale film and device integration.Atomic layer deposition (ALD) is a surface-controlled film fabrication and can provide a possible route towards the synthesis of TMD thin films since the ALD approach follows the layer-by-layer deposition mechanism [5,6]. As compared to the conventional CVD method, ALD can enable precise thickness control on atomic scale and excellent film uniformity as well as good stoichiometry and crystallinity with proper annealing steps. In this work, we employed the ALD-based synthesis method to grow wafer-scale MoS2 and WS2 thin films. Non-toxic MoCl5, WCl5 and hexamethyldisilathiane (HMDST) precursors have been used which are different and superior to those used in previous work. Film characterizations have confirmed the wafer-level uniformity, crystallinity and stoichiometry of the synthesized films. Homogeneous electrical behaviors have also been obtained from the fabricated FET device arrays. In addition, optoelectronic devices such as photodetectors and simple logic gates such as n-type inverter arrays have been demonstrated using the wafer-scale MoS2 FET arrays. Furthermore, we have used the substitutional doping in the ALD process to achieve controllable p-type doping of MoS2 films, which can provide solid basis for the complimentary metal-oxide-semiconductor (CMOS) integrated circuit applications. This work shows that the ALD-based synthesis of the 2D TMD thin films is an attractive approach and has provided a promising platform to further push forward the circuit and system level applications of the TMD materials.

Electrochemical measurement of respiratory activity for evaluation of fibroblast spheroids containing endothelial cell networks

Vascularized three-dimensional (3D) cultures such as spheroids overcome the problems of insufficient nutrient and oxygen supply and poor cell viability observed with non-vascularized spheroids. However, the capacity of drug penetration may differ with the presence of vascular structures, and needs to be evaluated. Co-culture of endothelial cells (ECs) with other cell types such as fibroblasts is one of the promising methods to engineer vascularized 3D tissue models. At a first step for fabricating vascularized tissues, it is important to prepare EC networks inside the tissue models. Here, we present the first attempt to apply electrochemical measurements of respiratory activity to the fibroblast spheroids containing EC networks, aiming to develop an evaluation technique for vascularized tissue models. The spheroids were exposed to doxorubicin (DOX), an inhibitor of DNA and RNA synthesis, to investigate their drug sensitivity that may differ with the presence of ECs, though rarely studied with regard to respiratory activity. Respiratory activity was measured using two electrochemical devices, a scanning electrochemical microscope (SECM) and a large scale integration (LSI)-based amperometric device. The fibroblast spheroids containing EC networks were constructed with a simple method involving co-culture of normal human dermal fibroblasts (NHDFs) and human umbilical vein endothelial cells (HUVECs) at different concentrations. Fluorescence images showed that HUVECs formed partially networked structure in the fibroblast spheroids. Respiratory activity of the spheroids as measured by SECM varied according to the proportion of HUVECs. In particular, the respiratory activity decreased more in spheroids with a larger proportion of HUVECs after DOX treatment, indicating that drug sensitivity of the spheroids became higher upon incorporation of EC networks. The results with the LSI device also corresponded to those with SECM. Overall, the electrochemical measurements provide meaningful information regarding the EC networks and play an important role in the analysis of 3D cell structures.

Combination of Double-Mediator System with Large-Scale Integration-Based Amperometric Devices for Detecting NAD(P)H:quinone Oxidoreductase 1 Activity of Cancer Cell Aggregates.

NAD(P)H:quinone oxidoreductase 1 (NQO1) is a key enzyme providing cytoprotection from quinone species. In addition, it is expressed at high levels in many human tumors, such as breast cancer. Therefore, it is considered to be a potential target in cancer treatment. In order to detect intracellular NQO1 activity in MCF-7 aggregates as a cancer model, we present, in this study, a double-mediator system combined with large-scale integration (LSI)-based amperometric devices. This LSI device contained 20 × 20 Pt working electrodes with a 250 μm pitch for electrochemical imaging. In the detection system, menadione (MD) and [Fe(CN)6]3- were used. Since MD can diffuse into cells due to its hydrophobicity, it is reduced into menadiol by intracellular NQO1. The menadiol diffuses out of the cells and reduces [Fe(CN)6]3- of a hydrophilic mediator into [Fe(CN)6]4-. The accumulated [Fe(CN)6]4- outside the cells is electrochemically detected at 0.5 V in the LSI device. Using this strategy, the intracellular NQO1 activity of MCF-7 aggregates was successfully detected. The effect of rotenone, which is an inhibitor for Complex I, on NQO1 activity was also investigated. In addition, NQO1 and respiration activities were simultaneously imaged using the detection system that was further combined with electrochemicolor imaging. Thus, the double-mediator system was proven to be useful for evaluating intracellular redox activity of cell aggregates.

Writing magnetic memory with ultrashort light pulses

Laser pulses are the shortest stimulus known to control the magnetization of materials and to switch magnetic devices on the picosecond to femtosecond timescales. Femtosecond laser pulses have been able to trigger the fastest changes in the magnetic state of matter, and thus these pulses may lead to technologies with increased speed and energy efficiency of magnetic data storage and memory. In the past decade, materials enabling optical control of magnetism and concepts of devices employing such opto-magnetic phenomena have been shown. In this Review, we explore ultrafast all-optical switching (AOS) of magnetization as the least-dissipative and fastest method for magnetic writing. We outline the physical processes responsible for mechanisms of AOS, define the materials suitable for optical control of magnetism and test these mechanisms and materials against three important criteria of recording: speed, accompanying dissipations and scalability. In particular, we emphasize that switching magnetization with the help of light outperforms other methods in terms of the speed of the write–read magnetic recording event (less than 20 ps) and the unprecedentedly low heat load (<6 J cm−3). Finally, we outline the integration of AOS in spintronic devices and the perspective of large-scale integration towards magnetic random access memory and other memory applications with low-energy dissipations. Laser pulses can trigger fast changes in magnetic state, facilitating new magnetic data storage and memory devices. This Review outlines the mechanisms of all-optical switching and the materials suitable for the optical control of magnetism and tests these mechanisms and materials in terms of speed, accompanying dissipations and scalability. Finally, the large-scale integration of devices in memory applications with low-energy dissipations is discussed.

Graphene-enabled and directed nanomaterial placement from solution for large-scale device integration

Directed placement of solution-based nanomaterials at predefined locations with nanoscale precision limits bottom-up integration in semiconductor process technology. We report a method for electric-field-assisted placement of nanomaterials from solution by means of large-scale graphene layers featuring nanoscale deposition sites. The structured graphene layers are prepared via either transfer or synthesis on standard substrates, and then are removed once nanomaterial deposition is completed, yielding material assemblies with nanoscale resolution that cover surface areas >1 mm2. In order to demonstrate the broad applicability, we have assembled representative zero-dimensional, one-dimensional, and two-dimensional semiconductors at predefined substrate locations and integrated them into nanoelectronic devices. Ultimately, this method opens a route to bottom-up integration of nanomaterials for industry-scale applications.

Local hydrogel fabrication based on electrodeposition with a large-scale integration (LSI)-based amperometric device

Addressable electrode arrays are widely used in a number of applications, such as electrochemical imaging and high-throughput assays. Recently, large-scale integration (LSI) technologies have been used to prepare electrochemical devices containing signal amplifiers and switching elements, such that multiple highly sensitive sensors can be incorporated into these devices. Because these devices induce chemical reactions at the target electrodes, biomaterials such as hydrogels can be electrochemically fabricated. In this study, we present a new biofabrication strategy using the electrochemical device. We used an LSI device to locally electrodeposit chitosan hydrogels at the target electrodes, with the goal of fabricating the designed hydrogels. The hydrogels were fabricated via the generation of Cl2 at the anodes where a potential of 0.95 V was applied. The biofabrication method was utilized for three bioapplications. First, three-dimensionally designed chitosan hydrogels, for example apple-shaped and layered hydrogels were fabricated on this device by electrodepositing them for 10–30 s. In order to demonstrate biosensing, glucose oxidase and horseradish peroxidase were modified at the target electrodes through hydrogel electrodeposition; consequently, droplets containing glucose and H2O2 were electrochemically imaged at the same time using the electrochemicolor imaging technique we developed. Since this system can be used to fabricate hydrogels containing enzymes only at the target sensors, glucose and H2O2 were separately monitored. The detection limit of glucose was less than 0.5 mM. In addition, the chitosan hydrogels were electrodeposited only in the target areas such that cells only adhering at unmodified areas, resulting in cell patterning. We show that the LSI device is useful for the fabrication of local hydrogels for several bioapplications such as biosensing and cell culturing.

Topologically protected edge transport of sound in coupled cavities of a modified honeycomb lattice

In this work, we investigate comprehensively the unidirectional transport of sound in coupled cavities of a modified honeycomb lattice. The results clearly show that a pair of topological states carrying opposite pseudospins can be constructed at the edge of truncated lattices of non-trivial band gaps, which is different from previous schemes where topological states with opposite pseudospins were constructed at the interface of modified honeycomb lattices of trivial and non-trivial band gaps. Our work paves the way to exploring unidirectional edge transport of sound with topological protection in closed systems that are beneficial in large-scale device integration and low-loss operation.

A 300-mm Silicon Photonics Platform for Large-Scale Device Integration

A 300-mm silicon photonics platform for large-scale device integration was developed, leveraging 40-nm complementary metal-oxide-semiconductor technology. Through fabrication using this technology platform, wire waveguides were obtained with low propagation losses for the C-band (0.4 dB/cm) and O-band (1.3 dB/cm). Several types of wavelength filters, including a coupled resonator optical waveguide (CROW), an arrayed waveguide grating, and a cascaded Mach–Zehnder interferometer, were also demonstrated, with low crosstalk and low insertion loss. A polarization rotator Bragg grating with multiple reflection peaks having polarization independence was also obtained. In terms of wafer-scale uniformity, a small standard deviation of 0.7 nm in resonant wavelength for the CROW was confirmed. A grating coupler also exhibited low wafer-scale variations in the maximum coupling efficiency and the diffraction wavelength in optical coupling with a single-mode fiber. Extraction of fabrication deviations for the waveguides was performed using the spectral variation of microring resonators and grating couplers. The extracted wafer-scale variations in waveguide width and height and grating depth well reproduced the results of physical measurements, with subnanometer-level accuracy. The developed technology can thus enable manufacturing of high-speed, low-power optical interconnects.

Formation of ultralong GaN nanowires up to millimeter length scale and photoconduction study in single nanowire

Long length GaN nanowire is emerging as desirable requirement for nanodevice applications including sensors, catalytic functionalities and large scale device integration. An alternate approach to obtain ultralong GaN nanowires with length up to millimeter is reported here. High quality ultralong GaN nanowires are obtained from β-Ga2O3 nanowires. As-formed ultralong GaN nanowires with bandgap of 3.4eV exhibit wurtzite crystal structure. The high quality of as-formed ultralong GaN nanowires has been confirmed by XRD, Raman, TEM and photoluminescence. The photoconduction in single ultralong GaN nanowire shows high responsivity in order of ~103 and gains in order of ~104.

Integrated On-Chip Nano-Optomechanical Systems

Recent developments in integrated on-chip nano-optomechanical systems are reviewed. Silicon-based nano-optomechanical devices are fabricated by a two-step process, where the first step is a foundry-enabled photonic circuits patterning and the second step involves in-house mechanical device release. We show theoretically that the enhanced responsivity of near-field optical transduction of mechanical displacement in on-chip nano-optomechanical systems originates from the finesse of the optical cavity to which the mechanical device couples. An enhancement in responsivity of more than two orders of magnitude has been observed when compared side-by-side with free-space interferometry readout. We further demonstrate two approaches to facilitate large-scale device integration, namely, wavelength-division multiplexing and frequency-division multiplexing. They are capable of significantly simplifying the design complexity for addressing individual nano-optomechanical devices embedded in a large array.

Coincidence Lattices and Interlayer Twist in van der Waals Heterostructures: Application of the Coincidence Lattice Method on $$\hbox {hBN/MoSe}_2$$ hBN/MoSe 2 Heterobilayer Systems

Van der Waals heterostructures have great potential in large-scale integration devices and exploration of new physics. Experimental investigations allow flexible combinations of two-dimensional crystals in device fabrications. Theory, however, has limitations of supercell sizes and commensurability, translated into computational effort. In this work, we demonstrate the application of the coincidence lattice method to simulate two \(\hbox {hBN/MoSe}_2\) heterobilayers taking interlayer twist effects into account. We predict that both systems are stable upon contact and interact via van der Waals dispersions. We found that electronic properties of \(\hbox {MoSe}_2\) are preserved for both simulated systems, but hBN suffers from the increase of interface interactions, as evidenced by band structures and density of states calculations. Finally, band discontinuities are obtained and charge transfer arguments explain small shifts in band offsets with respect to natural alignments. We conclude that hBN is a reasonable substrate for preserving useful properties of \(\hbox {MoSe}_2\) for application in electronic and optoelectronic devices, and that interlayer twist angles play a significant role in the physics of van der Waals heterostructures.

The micropatterning of layers of colloidal quantum dots with inorganic ligands using selective wet etching

The micropatterning of layers of colloidal quantum dots (QDs) stabilized by inorganic ligands is demonstrated using PbS core and CdSe/CdS core/shell QDs. A layer-by-layer approach is used to assemble the QD films, where each cycle involves the deposition of a QD layer by dip-coating, and the replacement of the native organic ligands by inorganic moieties, such as OH− and S2−, followed by a thorough cleaning of the resulting film. This results in a smooth and crack-free QD film on which a photoresist can be spun. The micropatterns are defined by a positive photoresist, followed by the removal of uncovered QDs by selective wet etching with an HCl/H3PO4 mixture. The resulting patterns can have submicron feature dimensions, limited by the resolution of the lithographic process, and can be formed on planar and 3D substrates. It is shown that the photolithography and wet etching steps have little effect on the photoluminescence quantum yield of CdSe/CdS QDs. Compared with the unpatterned CdSe/CdS QD film, only a 10% degradation in the quantum yield is observed. These results demonstrate the feasibility of the proposed micropatterning method to implement the large-scale device integration of colloidal quantum dots.

Deposition of a Continuous and Conformal Copper Seed Layer by a Large-Area Electron Cyclotron Resonance Plasma Source with Embedded Lisitano Antenna

To deposit copper seed layer on ultra large scale integration devices, a large-area (O 378 mm) electron cyclotron resonance plasma has been generated by using permanent magnets-embedded Lisitano antenna. The plasma source operates in the pressure range of 0.2–1.5 mTorr with microwave power range of 500–2,000 W. By using a Langmuir probe, the electron density and temperature have been measured near the DC sputter target position. Measurements indicate argon plasmas having electron densities of ~5 × 1010/cm and electron temperatures of 5 eV with 750 W microwave power at gas pressures of 0.5 mTorr. Using this plasma source and a DC sputter, we obtained excellent conformal copper seed layer with high aspect ratios of 12:1. This is in contrast with conventional methods using magnetron sputter, which has aspect ratios of 2–3:1. Also, improvements are observed in the smoothness (root mean square roughness of 1.345 nm), uniformity (2.5 % at 300 mm wafer), and sidewall symmetricity (more than 95 %) of the copper seed layer.

In Situ Repair of High-Performance, Flexible Nanocrystal Electronics for Large-Area Fabrication and Operation in Air

Colloidal semiconductor nanocrystal (NC) thin films have been integrated in light-emitting diodes, solar cells, field-effect transistors (FETs), and flexible, electronic circuits. However, NC devices are typically fabricated and operated in an inert environment since the reactive surface and high surface-to-volume ratio of NC materials render them sensitive to oxygen, water, and many solvents. This sensitivity has limited device scaling and large-scale device integration achievable by conventional fabrication technologies, which generally require ambient air and wet-chemical processing. Here, we present a simple, effective route to reverse the detrimental effects of chemical and environmental exposure, by incorporating, in situ, a chemical agent, namely, indium metal, which is thermally triggered to diffuse and repair the damage. Taking advantage of the recovery process, CdSe NC FETs are processed in air, patterned using the solvents of lithography, and packaged by atomic layer deposition to form large-area and flexible high-performance NC devices that operate stably in air.

Fabrication of Arrayed Si Nanowire-Based Nano-Floating Gate Memory Devices on Flexible Plastics

Arrayed Si nanowire (NW)-based nano-floating gate memory (NFGM) devices with Pt nanoparticles (NPs) embedded in Al2O3 gate layers are successfully constructed on flexible plastics by top-down approaches. Ten arrayed Si NW-based NFGM devices are positioned on the first level. Cross-linked poly-4-vinylphenol (PVP) layers are spin-coated on them as isolation layers between the first and second level, and another ten devices are stacked on the cross-linked PVP isolation layers. The electrical characteristics of the representative Si NW-based NFGM devices on the first and second levels exhibit threshold voltage shifts, indicating the trapping and detrapping of electrons in their NPs nodes. They have an average threshold voltage shift of 2.5 V with good retention times of more than 5 x 10(4) s. Moreover, most of the devices successfully retain their electrical characteristics after about one thousand bending cycles. These well-arrayed and stacked Si NW-based NFGM devices demonstrate the potential of nanowire-based devices for large-scale integration.