This report demonstrates an innovative method to achieve large scale 20 μm pitch Cu-Cu direct bonding, utilizing lithographic stencil printing to transfer small-sized nano-copper (CuNPs) paste and employs a thermocompression method for CuNPs sintering to establish interconnections between copper-pillars and CuNPs bumps. Shear tests were conducted to characterize the bonding strength. High-throughput 20 μm pitch copper-to-copper direct bonding enables lower annealing temperatures for bulk-Cu to bulk-Cu bonding. Lithographic stencil printing is used to transfer the CuNPs paste, followed by sintering of the nanoparticles to establish interconnections. Shear tests and cross-section SEM were conducted to characterize the bonding strength and quality.

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Power MOSFET dies in the automotive industry are becoming larger (>5 × 5 mm) and thinner (<50 µm) to meet high-performance and lifetime requirements. Ensuring the mechanical robustness of these large ultrathin chips is crucial for reliable electronic devices and high-throughput packaging processes. The high aspect ratio and advanced chip designs incorporating trench technology present significant challenges in semiconductor assembly, packaging, and testing. This paper introduces an experimental front-end strategy aimed at strengthening the front side (FS) of large ultrathin dies using various die-top systems. Industry-equivalent 50 µm thick dummy power MOSFET dies were fabricated to evaluate the efficacy of different chip designs and materials, such as polyimide (PI), in mitigating fracture risks. Fabrication-induced stresses and warpage in the device layers were measured using a thin-film stress measurement tool. Additionally, the FS strength of the ultrathin dies was assessed using the three-point bending method, with the resulting data analyzed via two-parameter Weibull distribution plots. Results demonstrated that the deposition of 5 µm PI on the nitride die topside significantly increased die strength from 339 MPa to 760 MPa, with 5 µm PI proving more effective for die strengthening than 10 µm. The interaction between the metal-trench layer and the die was found to be critical to the robustness of ultrathin dies, influenced by the pattern and layout of the trenches. Die-top metallization designs, such as meandering patterns, showed promising improvements in die strength compared to standard designs. A proposed chip layout aims to maximize PI coverage for clip-bonded products on the die topside, leveraging its strengthening effect. The study also demonstrated that dummy reference chips can facilitate rapid and straightforward evaluation of extensive design experiments to identify robust chip designs.

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Copper nanoparticles (CuNPs) sintering for flip-chip interconnects is a promising solution for 3D and heterogeneous integration to overcome the limitation of solder materials. To this end, we perform the photolithographic stencil printing method to pattern CuNPs, and the form of flip-chip interconnects is completed after CuNPs sintering process. This paper aims to study the effect of sintering processing parameters (time, pressure, temperature) on the mechanical properties of CuNPs bumps when applying the novel method to approach the Cu interconnects. We fabricated seven groups of specimens of sintered CuNPs bumps, built with a diameter of 100 μm and sintered. The nanoindentation tests assessed the mechanical property to get Young's modulus and hardness. Results clarify that Young's modulus is strongly affected by pressure. An suggested combination of parameters (the 25 MPa and 260 °C for 15 min) give the highest modulus of 126 GPa and the hardness of 1.76 GPa. Moreover, the observations by scanning electron microscopy (SEM) reveal the microstructure and porosity evolution versus different processing parameters.

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This study presents a novel manufacturing process and design towards an enhanced sensitivity of an in-package relative humidity sensor. The device comprises multi-width interdigital electrodes which make oxide pillars appear during wet chemical etching in the fabrication process. Those oxide pillars appear only in wider areas while completely etched away in narrower areas providing semi-floating metal fingers. Therefore, after wafer molding, the packaging encapsulation material such as the epoxy molding compound covers larger area around the electrodes and increases the sensitivity by confining more of the electrical field lines. The results confirm the enhanced sensitivity of the proposed humidity sensor for characterization and monitoring of the aging properties of packaging encapsulation materials.@en

Micro-devices that use electric fields to trap, analyze and inactivate micro-organisms vary in concept, design and application. The application of electric fields to manipulate and inactivate bacteria and single-celled organisms has been described extensively in the literature. By contrast, the effect of such fields on viruses is not well understood. This review explores the possibility of using existing methods for manipulating and inactivating larger viruses and bacteria, for smaller viruses, such as SARS-CoV-2. It also provides an overview of the theoretical background. The findings may be used to implement new ideas and frame experimental parameters that optimize the manipulation, sampling and inactivation of SARS-CoV-2 electrically. @en

The trend to 3D and heterogeneous integration enable driving multi-functional blocks in one package. Flip-chip integration is currently playing an important role and is based on solder joints. To overcome the limitations of solder joints, all-copper interconnects have been investigated to meet electrical, thermal, and reliability demands in 3D integration. The underfill process is widely applied in flip-chip encapsulation technology. We propose a novel wafer-scale all-Cu interconnect method combining epoxy-based photo-patternable polymer as self-aligned underfill layer with the patterned copper nanoparticles interconnects. The resulting test wafers were able to pattern 20 µm pitch copper nanoparticle-paste interconnects on both substrates with and without photoimageable polymer. The Cu paste was applied to form the interconnects and was sintered after bonding process. Free-standing nanocopper is sintered to obtain mechanical properties with a Young's modulus of 112 GPa. All-Cu interconnects with diameter of 50 µm and 100 µm were measured to achieve the specific contact resistance, ranging from 1.4 × 10-5O· cm2 to 1.0 × 10-5O· cm2 at different sintering temperature when epoxy-based underfill existing. And its resistivity was 4.54× 10-4 O· cm, compared to 5.86× 10-4O· cn for the all-Cu interconnects without underfill.

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This study presents the design and fabrication of an in-package relative humidity sensor for epoxy molding compound (EMC) packages. The sensor comprises shielded interdigital electrodes (SIDE) for in-situ monitoring of humidity absorption/desorption in the package encapsulation layer. A novel approach is employed in the device fabrication to maximize the electrical field lines to pass through the EMC and enhance the sensitivity. The manufactured wafer includes 6×6mm2 dies, each containing six identical capacitive sensors with an area of 480 × 620 μ m2. SU-8 through polymer vias (TPVs) with high aspect ratio were created to locally mold the sensors by EMC. The linear capacitance change with the relative humidity level is simulated in COMSOL Multiphysics. Three designs were compared, and the calibration results show the capacitance value of 1.54 pF and 5.85 pF before and after molding, respectively. The capacitance value stays within the range of 5.85 to 5.86 pF with less than 7 aF variation under different biasing voltages, indicating the stability and robustness of the capacitance.

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Wide bandgap (WBG) semiconductor technologies enable significant progress in the emergence of power modules. Power cycling at elevated temperatures causes crack or delamination failure, especially at the die-attached bonded interface in the long term. Therefore, the in-situ reliability investigation of power modules, materials, and semiconductor packages is of great significance for modern industries. The silicon carbide's higher bandgap energy, intrinsic thermal conductivity, and mechanical strength make it a great candidate for the next generation of semiconductor, designed to operate in harsh conditions. In this study, a thin-film reconfigurable silicon carbide (SiC) thermal test chip (TTC) is designed and fabricated for reliability assessment in harsh environments. The proposed TTC realizes in-situ power/thermal cycling tests at elevated temperatures as well as characterization of novel materials such as nanoparticle-based sintering materials in die-attach technology and high-temperature-compatible epoxy molding compounds. The chip is equipped with thin-film platinum microheaters to realize modular power mappings, and platinum resistive temperature detectors (RTD) to examine the thermal reliability by monitoring the precise changes of the internal junction-to-case thermal resistance.

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The thermal-piezoresistive effect in silicon (Si) has attracted great attention toward high-performance resonant devices but still faces major challenges for harsh environment applications. Instead of using Si, this paper, for the first time, reports a thermal-piezoresistive resonator based on a silicon carbide-on-insulator (SiCOI) platform. The resonance frequency simulation, CMOS-compatible fabrication, and thermoresistive properties characterization of the proposed SiCOI resonator are presented. The experimental results show linear current-voltage characteristics and a constant temperature coefficient of resistance (TCR) up to 200 °C.@en

Adhesive bonding is a key joining technology in many industrial applications, including automotive, aerospace industries, biomedical devices, and microelectronic components. Adhesive bonding is gaining more and more attention due to the increasing demand for joining similar or dissimilar components, mostly within the framework of designing lightweight structures. Silicone sealant is widely used in engineering application due to its thermal stability, excellent energy absorption, and good damping characteristics. In those applications, sealant usually exposed to various environment stress, such as, high temperature, mechanical stress, humidity, light radiation, and chemical attack. Long-term stability and durability of sealant is crucial to the performance of the associated application. The main degrading factors for silicone in microelectronic applications are temperature, humidity, alkali, and mechanical loading. The focus in the present paper is to understand different failure mechanisms in silicone sealants and adhesives and to study how different environmental, mechanical, and service-related stresses attribute to the kinetics and extent of degradation in silicone sealants and adhesives. The impact of different failure mechanisms on the lifetime and reliability of microelectronic devices will be methodically investigated.@en

This paper reports the design and fabrication of a 4H-SiC CMOS readout circuit enabling monolithic integration of silicon carbide (SiC) sensors and circuits. Compared to conventional Si electronics, 4H-SiC integrated circuits can sustain operation in harsh conditions such as higher temperatures and radiation levels. The proposed amplifier performance is well balanced through the temperature range of 25 °C to 400 °C. Compared to state-of-the-art, the proposed SiC readout circuit does not include any off-chip components. The amplifier is fully differential, and hence shows improved common-mode rejection and signal-to-noise ratio (SNR). It can be monolithically integrated with SiC sensors in a scalable SiC technology.@en

The rapid development of power electronics has challenged the thermal integrity of semiconductor packaging. Further developments in this domain can be supported significantly by utilizing fast and flexible thermal characteristic evaluation. This study employs the transient dual interface method (TDIM) to characterize and compare the thermal resistance of Ag- and Cu-sintered die-attach joints using an in-house developed thermal test chip (TTC). The proposed TTC with 82.5% active area achieves a temperature sensitivity of 12 Ω/K and maximum power of 360 W per cell, which are 50% and 44% higher than the state-of-the-art, respectively. The uniformity of the temperature distribution (1 °C at 68 W) is verified by infrared thermography. The cost-effective manufacturing process allows the design to be applied to any substrate, such as SiC or GaN. Ag and Cu sintering is performed to bond the TTC on a Cu substrate, and the junction-to-case thermal resistance of the sintered structures is extracted. The lowest junction-to-case thermal resistance of 0.144 K/W is measured for the device sintered using Ag paste. Meanwhile, the Cu sintered structure exhibits a comparable value of 0.158 K/W. The proposed TTC in combination with TDIM accelerates the introduction of novel and cost-effective materials such as Cu.@en

The next generation of satellites will need to tackle tomorrow's challenges for communication, navigation and observation. In order to do so, it is expected that the amount of satellites in orbit will keep increasing, form smart constellations and miniaturize individual satellites to make access to space cost effective. To enable this next generation of activities in space, it is vital to ensure the ability of these satellites to properly navigate themselves. This control starts with attitude measurement by the dedicated sensors on the satellite, commonly performed by sun position sensors. The state-of-the art is confronted by large signal distortions caused by light reflected by the Earth's albedo as well as keeping up with the satellite miniaturization trend. This work aims to address both these issues, by presenting a microfabricated albedo insensitive sun position sensor in silicon carbide with wafer-level integrated optics. The presented 10 mm×10 mm×1 mm system reaches a mean angular accuracy of 5.7° in a ±37° field-of-view and integrates an on-chip temperature sensor with a -3.9 mV K⁻¹ sensitivity in the 20 °C to 200 °C range.

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In this paper, we present a quadrant sun position sensor microsystem device in a silicon carbide technology that operates in a field-of-view of ±33° and reaches a mean error of 1.9° in this range. This will allow, for the first time, an inherently visible blind sun position sensor in a CMOS compatible technology. Opto-electronic integration of the photodetectors and CMOS readout circuitry on-chip is vital to compete with the performance of silicon state-of-the-art and for the concept to be adopted by industry, which is where previous implementations of visible blind sun sensors are lacking.@en

The wide bandgap of silicon carbide (SiC) has attracted a large interest over the past years in many research fields, such as power electronics, high operation temperature circuits, harsh environmental sensing, and more. To facilitate research on complex integrated SiC circuits, ensure reproducibility, and cut down cost, the availability of a low-voltage SiC technology for integrated circuits is of paramount importance. Here, we report on a scalable and open state-of-the-art SiC CMOS technology that addresses this need. An overview of technology parameters, including MOSFET threshold voltage, subthreshold slope, slope factor, and process transconductance, is reported. Conventional integrated digital and analog circuits, ranging from inverters to a 2-bit analog-to-digital converter, are reported. First yield predictions for both analog and digital circuits show great potential for increasing the amount of integrated devices in future applications.

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This work demonstrates the first on-chip UV optoelectronic integration in 4H-SiC CMOS, which includes an image sensor with 64 active pixels and a total of 1263 transistors on a 100 mm2 chip. The reported image sensor offers serial digital, analog, and 2-bit ADC outputs and operates at 0.39 Hz with a maximum power consumption of 60 μW, which are significant improvements over previous reports. UV optoelectronics have applications in flame detection, satellites, astronomy, UV photography, and healthcare. The complexity of this optoelectronic system paves the way for new applications such harsh environment microcontrollers.@en

The continuous trend to integrate more multi-functions in a package often involves, Heterogeneous Integration of multi-functional blocks in some kind of 3D stacking. The conventional flip chip for die-on-substrate technology applies solder for integration. However, solder joint integration has the disadvantages of restricting height, reflow issues and re-melting at high operating temperatures. Nanometallic particle sintering offers a potential solution for these solder related issues. Nanometallic particle sintering occurs at low temperature and does not reflow and melt at higher temperatures. Hence, it can be applied for quite precise alignment and integration technologies, such as photonic components on silicon for harsh environment applications. In order to test this concept, we use sapphire and Si wafers with different mechanical properties, which can lead to the coefficient of thermal expansion mismatch. The sapphire chip can operate at a higher temperature applied for ultraviolet photonics application. This report describes a novel approach using copper nanoparticles paste patterned through photolithographic stencil printing. The photoresist acts as the stencil mask, and a photoresist lift-off process is applied to strip the photoresist stencil. This process has the advantages of lithographic form factor and precision and provides a chip to chip interconnect with a standard height of 20 µm.@en

Advances in semiconductor device manufacturing technologies are enabled by the development and application of novel materials. Especially one class of materials, nanoporous films, became building blocks for a broad range of applications, such as gas sensors and interconnects. Therefore, a versatile fabrication technology is needed to integrate these films and meet the trend towards device miniaturization and high integration density. In this study, we developed a novel method to pattern nanoporous thin films with high flexibility in material selection. Herein, Au and ZnO nanoparticles were synthesized by spark ablation and printed on a Ti/TiO2 adhesion layer, which was exposed by a lithographic stencil mask. Subsequently, the photoresist was stripped by a cost-efficient lift-off process. Nanoporous patterned features were thus obtained and the finest feature has a gap width of 0.6 μ fm and a line width of 2 μ fm. Using SEM and profilometers to investigate the structure of the films, it was demonstrated that the lift-off process had a minor impact on the microstructure and thickness. The samples presented a rough surface and high porosity, indicating a large surface-to-volume ratio. This is supported by the measured conductivity of Au nanoporous film, which is 12% of the value for bulk Au. As lithographic stencil printing is compatible with conventional lithographic pattering, this method enables further application on mass production of various nanoporous film-based devices in the future.

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High-performance IC-to-antenna interconnection is one of the key enablers for the mass production of high-end millimeter wave (mmW) radar systems above 100 GHz. In this work, a radar system with an on-package antenna array working at 122 GHz is presented. The antenna is placed on top of the molded package and the antenna-to-chip interconnection is realized by through-polymer via (TPV) technology. The detailed fabrication process of the radar antenna-in-package (AiP) with TPV is discussed. The results from the functional tests of the radar AiP are presented and benchmarked to a commercial quad-flat no-leads (QFN) package with an open antenna cavity. The detection margin between the echo signal and the constant false alarm rate (CFAR) threshold is approximately 10 dB higher for the TPV radar AiP compared with the benchmarked commercial QFN package.@en

With an increasing demand for high-power electronics, the need to meet stringent automotive norms and better understand the critical failure mechanisms are crucial in order to improve their reliablity. To that end, we developed an in-situ reliability monitoring setup capable of actively measuring the thermal performance of the package during lifetime testing. A Thermal Test Chip (TTC) assembled into a Power Quad Flat No-lead (PQFN) package was employed as a test vehicle for non-destructive reliability assessment. The TTC comprises resistive heaters as a heat source and resistive temperature elements for measuring the thermal response. The transient thermal behavior was evaluated based on the contribution of heat source to a temperature field, and the temperature distribution was measured at multiple spatial positions. The experimental results provide insights into the thermal properties’ influence on the thermal behavior of the package. A compact electro-thermal model based on analogies was developed to deconvolute and analyze the transient thermal measurements. The results of the compact model correlate with the experimental measurements, and the model’s accuracy was verified using finite element simulations. The development of such thermal characterization experiments and computationally inexpensive models assist in further understanding the impact of failures in advancing high-power density electronics.@en