Remote Epitaxy: Fundamentals, Challenges, and Opportunities.

Advanced heterogeneous integration technologies are pivotal for next-generation electronics. Single-crystalline materials are one of the key building blocks for heterogeneous integration, although it is challenging to produce and integrate these materials. Remote epitaxy is recently introduced as a solution for growing single-crystalline thin films that can be exfoliated from host wafers and then transferred onto foreign platforms. This technology has quickly gained attention, as it can be applied to a wide variety of materials and can realize new functionalities and novel application platforms. Nevertheless, remote epitaxy is a delicate process, and thus, successful execution of remote epitaxy is often challenging. Here, we elucidate the mechanisms of remote epitaxy, summarize recent breakthroughs, and discuss the challenges and solutions in the remote epitaxy of various material systems. We also provide a vision for the future of remote epitaxy for studying fundamental materials science, as well as for functional applications.

Mixed-Dimensional Integration of 3D-on-2D Heterostructures for Advanced Electronics.

Two-dimensional (2D) materials have garnered significant attention due to their exceptional properties requisite for next-generation electronics, including ultrahigh carrier mobility, superior mechanical flexibility, and unusual optical characteristics. Despite their great potential, one of the major technical difficulties toward lab-to-fab transition exists in the seamless integration of 2D materials with classic material systems, typically composed of three-dimensional (3D) materials. Owing to the self-passivated nature of 2D surfaces, it is particularly challenging to achieve well-defined interfaces when forming 3D materials on 2D materials (3D-on-2D) heterostructures. Here, we comprehensively review recent progress in 3D-on-2D incorporation strategies, ranging from direct-growth- to layer-transfer-based approaches and from non-epitaxial to epitaxial integration methods. Their technological advances and obstacles are rigorously discussed to explore optimal, yet viable, integration strategies of 3D-on-2D heterostructures. We conclude with an outlook on mixed-dimensional integration processes, identifying key challenges in state-of-the-art technology and suggesting potential opportunities for future innovation.

Heterogeneous Integration of Memristive and Piezoresistive MDMO-PPV-Based Copolymers in Nociceptive Transmission with Fast and Slow Pain for an Artificial Pain-Perceptual System.

Nociceptive pain perception is a remarkable capability of organisms to be aware of environmental changes and avoid injury, which can be accomplished by specialized pain receptors known as nociceptors with 4 vital properties including threshold, no adaptation, relaxation, and sensitization. Bioinspired systems designed using artificial devices are investigated to imitate the efficacy and functionality of nociceptive transmission. Here, an artificial pain-perceptual system (APPS) with a homogeneous material and heterogeneous integration is proposed to emulate the behavior of fast and slow pain in nociceptive transmission. Retention-differentiated poly[2-methoxy-5-(3,7-dimethyoctyoxyl)-1,4-phenylenevinylene] (MDMO-PPV) memristors with film thicknesses of 160 and 80 nm are manufactured and adopted as A-δ and C nerve fibers of nociceptor conduits, respectively. Additionally, a nociceptor mimic, the ruthenium nanoparticles (Ru-NPs)-doped MDMO-PPV piezoresistive pressure sensor, is fabricated with a noxiously stimulated threshold of 150 kPa. Under the application of pricking and dull noxious stimuli, the current flows predominantly through the memristor to mimic the behavior of fast and slow pain, respectively, in nociceptive transmission with postsynaptic potentiation properties, which is analogous to biological pain perception. The proposed APPS can provide potential advancements in establishing the nervous system, thus enabling the successful development of next-generation neurorobotics, neuroprosthetics, and precision medicine.

Heterogeneous micro-architectonic integration of SU-8 and highly entangled polyacrylamide hydrogel to realize cut-resistant soft superhydrophobic surfaces.

This paper presents a novel idea to create cut-resistant superhydrophobic (SHPo) surfaces by integrating an array of SU-8 micropillars on a highly entangled polyacrylamide (PAAm) hydrogel substrate. We begin by demonstrating that this highly entangled PAAm hydrogel exhibits superior resistance to cutting while being as transparent, flexible, and stretchable as other polymeric substrates like polydimethylsiloxane (PDMS). Currently, there are no well-known methods or chemicals to directly integrate SU-8 and PAAm with a covalent bond. To overcome this challenge, we introduce a thin layer of chemically modified PDMS between the SU-8 and PAAm so that covalent bonds can be formed between both the SU-8/PDMS interface and the PDMS/PAAm interface. After validating the reliability of the bonding in our experiments, we develop a heterogeneous integration process to fabricate the desired SHPo surface. To demonstrate the critical role of PAAm hydrogel in achieving the cut-resistant SHPo surface, we contrast this new SHPo surface with a reference version that uses a PDMS substrate instead. We conduct microscopic inspections using scanning electron microscopy (SEM) and a contact angle goniometer before and after cutting the two surfaces. These evaluations show significant differences in their structural integrity and behavior in water interaction.

Design and Fabrication of a Thin and Micro-Optical Sensor for Rapid Prototyping.

Optical sensing offers several advantages owing to its non-invasiveness and high sensitivity. The miniaturization of optical sensors will mitigate spatial and weight constraints, expanding their applications and extending the principal advantages of optical sensing to different fields, such as healthcare, Internet of Things, artificial intelligence, and other aspects of society. In this study, we present the development of a miniature optical sensor for monitoring thrombi in extracorporeal membrane oxygenation (ECMO). The sensor, based on a complementary metal-oxide semiconductor integrated circuit (CMOS-IC), also serves as a photodiode, amplifier, and light-emitting diode (LED)-mounting substrate. It is sized 3.8 × 4.8 × 0.75 mm3 and provides reflectance spectroscopy at three wavelengths. Based on semiconductor and microelectromechanical system (MEMS) processes, the design of the sensor achieves ultra-compact millimeter size, customizability, prototyping, and scalability for mass production, facilitating the development of miniature optical sensors for a variety of applications.

Heterogeneous Integration of Atomically Thin Semiconductors for Non-von Neumann CMOS.

Atomically thin, 2D, and semiconducting transition metal dichalcogenides (TMDs) are seen as potential candidates for complementary metal oxide semiconductor (CMOS) technology in future nodes. While high-performance field effect transistors (FETs), logic gates, and integrated circuits (ICs) made from n-type TMDs such as MoS2 and WS2 grown at wafer scale have been demonstrated, realizing CMOS electronics necessitates integration of large area p-type semiconductors. Furthermore, the physical separation of memory and logic is a bottleneck of the existing CMOS technology and must be overcome to reduce the energy burden for computation. In this article, the existing limitations are overcome and for the first time, a heterogeneous integration of large area grown n-type MoS2 and p-type vanadium doped WSe2 FETs with non-volatile and analog memory storage capabilities to achieve a non-von Neumann 2D CMOS platform is introduced. This manufacturing process flow allows for precise positioning of n-type and p-type FETs, which is critical for any IC development. Inverters and a simplified 2-input-1-output multiplexers and neuromorphic computing primitives such as Gaussian, sigmoid, and tanh activation functions using this non-von Neumann 2D CMOS platform are also demonstrated. This demonstration shows the feasibility of heterogeneous integration of wafer scale 2D materials.

Flexible electronic/optoelectronic microsystems with scalable designs for chronic biointegration.

Flexible biocompatible electronic systems that leverage key materials and manufacturing techniques associated with the consumer electronics industry have potential for broad applications in biomedicine and biological research. This study reports scalable approaches to technologies of this type, where thin microscale device components integrate onto flexible polymer substrates in interconnected arrays to provide multimodal, high performance operational capabilities as intimately coupled biointerfaces. Specificially, the material options and engineering schemes summarized here serve as foundations for diverse, heterogeneously integrated systems. Scaled examples incorporate >32,000 silicon microdie and inorganic microscale light-emitting diodes derived from wafer sources distributed at variable pitch spacings and fill factors across large areas on polymer films, at full organ-scale dimensions such as human brain, over ∼150 cm2 In vitro studies and accelerated testing in simulated biofluids, together with theoretical simulations of underlying processes, yield quantitative insights into the key materials aspects. The results suggest an ability of these systems to operate in a biologically safe, stable fashion with projected lifetimes of several decades without leakage currents or reductions in performance. The versatility of these combined concepts suggests applicability to many classes of biointegrated semiconductor devices.

A Roadmap for Disruptive Applications and Heterogeneous Integration Using Two-Dimensional Materials: State-of-the-Art and Technological Challenges.

This Mini Review attempts to establish a roadmap for two-dimensional (2D) material-based microelectronic technologies for future/disruptive applications with a vision for the semiconductor industry to enable a universal technology platform for heterogeneous integration. The heterogeneous integration would involve integrating orthogonal capabilities, such as different forms of computing (classical, neuromorphic, and quantum), all forms of sensing, digital and analog memories, energy harvesting, and so forth, all in a single chip using a universal technology platform. We have reviewed the state-of-the-art 2D materials such as graphene, transition metal dichalcogenides, phosphorene and hexagonal boron nitride, and so forth, and how they offer unique possibilities for a range of futuristic/disruptive applications. Besides, we have discussed the technological and fundamental challenges in enabling such a universal technology platform, where the world stands today, and what gaps are required to be filled.

Spalling-Induced Liftoff and Transfer of Electronic Films Using a van der Waals Release Layer.

Heterogeneous integration strategies are increasingly being employed to achieve more compact and capable electronics systems for multiple applications including space, electric vehicles, and wearable and medical devices. To enable new integration strategies, the growth and transfer of thin electronic films and devices, including III-nitrides, metal oxides, and 2D materials, using 2D boron nitride (BN)-on-sapphire templates are demonstrated. The van der Waals (vdW) BN layer, in this case, acts as a preferred mechanical release layer for precise separation at the substrate-film interface and leaves a smooth surface suitable for vdW bonding. A tensilely stressed Ni layer sputtered on top of the film induces controlled spalling fracture that propagates at the BN/sapphire interface. By incorporating controlled spalling, the process yield and sensitivity are greatly improved, owed to the greater fracture energy provided by the stressed metal layer relative to a soft tape or rubber stamp. With stress playing a critical role in this process, the influence of residual stress on detrimental cracking and bowing is investigated. Additionally, a back-end selected area lift-off technique is developed which allows for isolation and transfer of individual devices or arbitrary shapes.

3D Photon-to-Digital Converter for Radiation Instrumentation: Motivation and Future Works.

Analog and digital SiPMs have revolutionized the field of radiation instrumentation by replacing both avalanche photodiodes and photomultiplier tubes in many applications. However, multiple applications require greater performance than the current SiPMs are capable of, for example timing resolution for time-of-flight positron emission tomography and time-of-flight computed tomography, and mitigation of the large output capacitance of SiPM array for large-scale time projection chambers for liquid argon and liquid xenon experiments. In this contribution, the case will be made that 3D photon-to-digital converters, also known as 3D digital SiPMs, have a potentially superior performance over analog and 2D digital SiPMs. A review of 3D photon-to-digital converters is presented along with various applications where they can make a difference, such as time-of-flight medical imaging systems and low-background experiments in noble liquids. Finally, a review of the key design choices that must be made to obtain an optimized 3D photon-to-digital converter for radiation instrumentation, more specifically the single-photon avalanche diode array, the CMOS technology, the quenching circuit, the time-to-digital converter, the digital signal processing and the system level integration, are discussed in detail.

[Technical Realization of Integrating Bone Age Artificial Intelligence Assessment System with Hospital RIS-PACS Network].

OBJECTIVE: To explore the integration method and technical realization of artificial intelligence bone age assessment system with the hospital RIS-PACS network and workflow. METHODS: Two sets of artificial intelligence based on bone age assessment systems (CHBoneAI 1.0/2.0) were developed. The intelligent system was further integrated with RIS-PACS based on the http protocol in Python flask web framework. RESULTS: The two sets of systems were successfully integrated into the local network and RIS-PACS in hospital. The deployment has been smoothly running for nearly 3 years. Within the current network setting, it takes less than 3 s to complete bone age assessment for a single patient. CONCLUSIONS: The artificial intelligence based bone age assessment system has been deployed in clinical RIS-PACS platform and the "running in parallel", which is marking a success of Stage-I and paving the way to Stage-II where the intelligent systems can evolve to become more powerful in particular of the system self-evolution and the "running alternatively".

Engineering the Size Distributions of Ordered GaAs Nanowires on Silicon.

Reproducible integration of III-V semiconductors on silicon can open new path toward CMOS compatible optoelectronics and novel design schemes in next generation solar cells. Ordered arrays of nanowires could accomplish this task, provided they are obtained in high yield and uniformity. In this work, we provide understanding on the physical factors affecting size uniformity in ordered GaAs arrays grown on silicon. We show that the length and diameter distributions in the initial stage of growth are not much influenced by the Poissonian fluctuation-induced broadening, but rather are determined by the long incubation stage. We also show that the size distributions are consistent with the double exponential shapes typical for macroscopic nucleation with a large critical length after which the nanowires grow irreversibly. The size uniformity is dramatically improved by increasing the As4 flux, suggesting a new path for obtaining highly uniform arrays of GaAs nanowires on silicon.

Conformal piezoelectric energy harvesting and storage from motions of the heart, lung, and diaphragm.

Here, we report advanced materials and devices that enable high-efficiency mechanical-to-electrical energy conversion from the natural contractile and relaxation motions of the heart, lung, and diaphragm, demonstrated in several different animal models, each of which has organs with sizes that approach human scales. A cointegrated collection of such energy-harvesting elements with rectifiers and microbatteries provides an entire flexible system, capable of viable integration with the beating heart via medical sutures and operation with efficiencies of ∼2%. Additional experiments, computational models, and results in multilayer configurations capture the key behaviors, illuminate essential design aspects, and offer sufficient power outputs for operation of pacemakers, with or without battery assist.

Selective-Area Growth of InAs Nanowires on Ge and Vertical Transistor Application.

III-V compound semiconductor and Ge are promising channel materials for future low-power and high-performance integrated circuits. A heterogeneous integration of these materials on the same platform, however, raises serious problem owing to a huge mismatch of carrier mobility. We proposed direct integration of perfectly vertically aligned InAs nanowires on Ge as a method for new alternative integrated circuits and demonstrated a high-performance InAs nanowire-vertical surrounding-gate transistor. Virtually 100% yield of vertically aligned InAs nanowires was achieved by controlling the initial surface of Ge and high-quality InAs nanowires were obtained regardless of lattice mismatch (6.7%). The transistor performance showed significantly higher conductivity with good gate control compared to Si-based conventional field-effect transistors: the drain current was 0.65 mA/µm, and the transconductance was 2.2 mS/µm at drain-source voltage of 0.50 V. These demonstrations are a first step for building alternative integrated circuits using vertical III-V/multigate planar Ge FETs.

Wafer-level heterogeneous integration of electrochemical devices and semiconductors for a monolithic chip.

Micro-scale electrochemical devices, despite their wide applications and unique potential to achieve 'More than Moore's law', face significant limitations in constructing functional chips due to their inability to integrate with semiconductors. In this study, we propose an electrochemical gating effect and material work function matching criteria, and thus establish the first heterogeneous integration theory for electrochemical devices and semiconductors. Accordingly, we create a novel 3D integration architecture and CMOS-compatible fabrication methodology, including optimizing individual devices, electron/ionic isolation, interconnection, and encapsulation. As a demonstration, we integrate electrochemical micro supercapacitors with a P-N junction diode rectifier bridge circuit and successfully obtain the first monolithic rectifier-filter chip, which shows a revolutionary volume reduction of 98% compared to non-integrateable commercial products. The chip can provide a stable output with a tiny ripple factor of 0.23% in typical conditions, surpassing the requirements of most applications by more than one order of magnitude. More importantly, all the processes are suitable for mass production in standard foundries, allowing ubiquitous applications of electrochemistry in integrated electronics.

Metal Nanoparticles Assisted Ultrafast Laser Plasmonic Microwelding of Oxide-Semiconductor Interconnects.

Integration of wafer-scale oxide and semiconductor materials meets the difficulties of residual stress and materials incompatibility. In this work, Ag NPs thin film is contributed as an energy confinement layer between oxide (Sapphire) and semiconductor (Si) wafers to localize the materials interaction during ultrafast laser irradiation. Due to the plasmonic effects generated within constructed dielectric-metal-dielectric structures (i.e., Sapphire-Ag-Si), thermal diffusion and chemical reaction between Ag and its neighboring materials facilitate the microwelding of Sapphire and Si wafers. Ag NPs can be totally sintered within the junction area to bridge oxide and semiconductor, while Al─O─Ag bond and Ag─Si bond are formed at Ag-Sapphire and Ag─Si interfaces, respectively. As-received heterogeneous joint exhibits a high shear strength up to 5.4 MPa, with the fracture occurring inside Si wafer. Meanwhile, insertion of metal nanolayer can greatly relieve the residual stress-induced microcracking inside the brittle materials. Such wafer-scale Sapphire and Si interconnects thus show robust strength and excellent impermeability even after thermal shocking (-40 °C to 120 °C) for 200 cycles. This metal NPs layer-assisted plasmonic microwelding technology can extend to broad materials integration, which is promising for high-performance microdevices development in MEMS, MOEMS, or microfluidics.

Uniform, Fully Connected, High-Quality Monocrystalline Freestanding Perovskite Oxide Films Fabricated from Recyclable Substrates.

Releasing epitaxial perovskite oxide films from their native oxide substrates produces high quality, 2D-material-like monocrystalline freestanding oxide membranes, as potential key components for the next-generation electronic devices. Two major obstacles still limit their practical applications: macroscopic material defects (mainly cracks) that lowers uniformity and yield, and the high cost of the consumed oxide substrates. Here, a two-step film transfer method and a substrate recycling method enable repetitive fabrication of millimeter-scale, fully-connected freestanding oxide films of various chemical compositions from the same substrates; arrays of capacitor and resistor devices based on these oxides transferred on silicon indicate high uniformity, low sample-to-sample variation, and satisfactory electrical connectivity. The two-step transfer suppresses crack formation by avoiding buckling-delamination-type relaxation of epitaxial strain, and the key point to achieve substrate reuse is to remove the residual Al species bonded to the substrate surfaces. The mitigation of such long-lasting issues in freestanding oxide fabrication techniques may eventually pave roads toward future industrial-grade devices, as well as enabling many research opportunities in fundamental physics.

Hybrid Molecular Beam Epitaxy for Single-Crystalline Oxide Membranes with Binary Oxide Sacrificial Layers.

The advancement in thin-film exfoliation for synthesizing oxide membranes has led to possibilities for creating artificially assembled heterostructures with structurally and chemically incompatible materials. The sacrificial layer method is a promising approach to exfoliate as-grown films from a compatible material system, allowing for their integration with dissimilar materials. Nonetheless, the conventional sacrificial layers often possess an intricate stoichiometry, thereby constraining their practicality and adaptability, particularly when considering techniques such as molecular beam epitaxy (MBE). This is where easy-to-grow binary alkaline-earth-metal oxides with a rock salt crystal structure are useful. These oxides, which include (Mg, Ca, Sr, Ba)O, can be used as a sacrificial layer covering a much broader range of lattice parameters compared to conventional sacrificial layers and are easily dissolvable in deionized water. In this study, we show the epitaxial growth of the single-crystalline perovskite SrTiO3 (STO) on sacrificial layers consisting of crystalline SrO, BaO, and Ba1-xCaxO films, employing a hybrid MBE method. Our results highlight the rapid (≤5 min) dissolution of the sacrificial layer when immersed in deionized water, facilitating the fabrication of millimeter-sized STO membranes. Using high-resolution X-ray diffraction, atomic-force microscopy, scanning transmission electron microscopy, impedance spectroscopy, and scattering-type near-field optical microscopy (SNOM), we demonstrate single-crystalline STO membranes with bulk-like intrinsic dielectric properties. The employment of alkaline earth metal oxides as sacrificial layers is likely to simplify membrane synthesis, particularly with MBE, thus expanding the research and application possibilities.

Extremely Low Thermal Resistance of ß-Ga2O3 MOSFETs by Co-integrated Design of Substrate Engineering and Device Packaging.

Gallium oxide (Ga2O3) emerges as a promising ultrawide bandgap semiconductor, which is expected to surpass the performance of current wide bandgap materials, like GaN and SiC, in electronic devices. However, widespread application of Ga2O3 is hindered by its extremely low thermal conductivity and lack of effective device-level thermal management strategies. In this work, Ga2O3 metal-oxide-semiconductor field-effect transistors (MOSFETs) are fabricated by conducting co-integrated design of substrate engineering with layer transferring and device packaging. 3D Raman thermography is introduced as a novel method to analyze the temperature distribution within the device, which provides valuable insights into their thermal performances. A high-quality Ga2O3-SiC heterogeneous integrated material is successfully fabricated with an extremely low interface thermal resistance of 6.67 ± 2 m2·K/GW. Compared to the homoepitaxial Ga2O3 MOSFETs, the degradation of Ion/Ioff in Ga2O3-SiC MOSFETs is decreased by 1.5 orders of magnitude, and that of Ron is decreased by 31%, showing the great thermal stability of Ga2O3-SiC MOSFETs. With the additional device packaging, a significant one order-of-magnitude reduction in the thermal resistance of the Ga2O3-SiC MOSFET is achieved, reaching a record-low value of 4.45 K·mm/W in the reported Ga2O3 MOSFETs. This work demonstrates an efficient strategy for device-level thermal management in next-generation Ga2O3 power and RF applications.

Van der Waals Epitaxial Growth of Ultrathin Indium Antimonide on Arbitrary Substrates through Low-Thermal Budget.

III-V semiconductors possess high mobility, high frequency response, and detection sensitivity, making them potentially attractive for beyond-silicon electronics applications. However, the traditional heteroepitaxy of III-V semiconductors is impeded by a significant lattice mismatch and the necessity for extreme vacuum and high temperature conditions, thereby impeding their in situ compatibility with flexible substrates and silicon-based circuits. In this study, a novel approach is presented for fabricating ultrathin InSb single-crystal nanosheets on arbitrary substrates with a thickness as thin as 2.4 nm using low-thermal-budget van der Waals (vdW) epitaxy through chemical vapor deposition (CVD). In particular, in situ growth has been successfully achieved on both silicon-based substrates and flexible polyimide (PI) substrates. Notably, the growth temperature required for InSb nanosheets (240 °C) is significantly lower than that employed in back-end-of-line processes (400 °C). The field effect transistor devices based on fabricated ultrathin InSb nanosheets exhibit ultra-high on-off ratio exceeding 108 and demonstrate minimal gate leakage currents. Furthermore, these ultrathin InSb nanosheets display p-type characteristics with hole mobilities reaching up to 203 cm2 V-1 s-1 at room temperatures. This study paves the way for achieving heterogeneous integration of III-V semiconductors and facilitating their application in flexible electronics.