Session D13: Industrial Microelectronics, Manufacturing, and Nanotechnology

Integrated 3D microlenses for efficient light extraction from diamond quantum emitters using two-photon polymerization

Quantum emitters in solid-state hosts such as nitrogen-vacancy (NV) centers in diamond have emerged as a robust platform in various applications such as quantum computing, nanoscale metrology, and biological sensing. A high photon collection efficiency is a key requirement for all these applications. However, photon collection is severely hampered by the high refractive index of diamond (2.4) at visible wavelengths which traps photons by total internal reflection. Previously, this problem has been addressed by the fabrication of monolithic photonic structures such as solid-immersion and metalenses in diamond. However, these approaches are inherently complex, expensive, lack scalability, and are destructive. Here, we present a fast, scalable, and non-destructive process for the fabrication of polymer microlenses on a diamond substrate using two-photon polymerization. Using this process, we present the fabrication of hemispherical and hyperboloid three-dimensional micro-optical elements. The fidelity of fabricated structures is confirmed by scanning electron microscopy. The characterization is carried out using a custom-built confocal microscope. We demonstrate an enhancement in collected photoluminescence and an improvement in the acquisition speed of optically detected magnetic resonance (ODMR) from NV centers. These results open the possibility of using polymer micro-optical elements for scalable quantum applications.   

Computation of Polyimine Membrane as an Alternative Absorbent for Enhanced CO2 Direct Air Capture

Direct Air Capture (DAC) of CO2 using solid-supported amines offers a promising strategy to address the escalating atmospheric carbon levels. While poly(ethylenimine) (PEI) has attracted significant attention due to its remarkable CO2 adsorption efficiency and stability, our study redirects the focus to poly(propylenimine) (PPI) and its hyperbranched form as potential alternative absorbents. Together with the PEI study, we primarily examine the distribution and transport behavior of CO2 molecules within these polymer systems under varying hydration conditions. Our results indicate that the pair correlations between CO2 and both primary and secondary amines in polyimines are reduced under hydrated conditions, suggesting a diminished role of the carbamate formation mechanism compared to the dry conditions. The diffusion behavior of CO2 is more restricted in PPI, as evidenced by its longer carbon backbone when juxtaposed with PEI simulation outcomes. We further explore the complexities of CO2 transport within these polymer systems when combined with rigid supporting material (MCM-41). For this study, we optimized new force field parameters using first-principle calculations. By elucidating local structures and molecular diffusion processes, particularly in contexts with different water content levels, we expand the understanding of CO2 capture mechanisms in amine-supported materials. Our findings not only bolster the existing knowledge base but also chart a course for discovering innovative materials and enhancing current DAC technologies.   

Effective Band Structure of β-Ga2O3 Alloys Towards Opto-electronic Applications: A First Principles Study

Metal oxide semiconductors have been intensively investigated for many applications, such as high-power electronics and solar-blind photodetectors. Despite this intense research, achieving p-type doping in Ga₂O₃ is still challenging, and presents a practical obstacle to the fabrication of p-n based devices. Alloying, e.g., with Al or In, is a promising strategy for engineering Ga₂O₃ structural and optoelectronic properties. Furthermore, incorporating Bi or Ni through alloying can yield an alternative route to p-type doping.

In this study, we investigate InGaO alloys by means of first principles using special quasi-random structures to model the substitutional disorder. The effective band structure of InGaO alloys reveals a systematic reduction of the band gap and electron effective mass as the In content is increased. In view of applications, the mechanical properties of InGaO alloys grown over β-Ga₂O₃ surfaces have been also investigated. Results are interpreted based on the site occupation preference of In atoms. Finally, we discuss the recent proposal of alloying Ga₂O₃ to engineer the band gap, pushing up the valence-band maximum and facilitating the acquisition of shallow acceptor states to achieve p-type doping.   

Hybrid Packaging: Flexible circuit integration for modern IC package technology.

As electronics continue to transition to flexible and/or conformal design spaces, modern IC integration has similarly become increasingly complex. To meet the needs of these new packaging paradigms, one must similarly expand the capabilities of additive manufacturing techniques. To overcome these challenges, we present a packaging system that combines printed encapsulants, mechanical design, and multi-dimensional material integration for robust printed interconnects operating at frequencies ranging from DC to X-band. The proposed methods and materials have demonstrated increased stability and resilience on flexible heterogeneous circuits with discreate passive components and modern IC packages. Additionally, we demonstrate integration of fine pitch packages such as micro ball grid array (μBGA), wafer-level packaging (WLP), and quad flat no-lead (QFN) on a variety of substrates including Kapton, UHMWPE composite, and RF laminate (I-Tera MT40). As a case-study demonstration, we analyzed the integration of pre-packaged ICs with printed RF circuits using an adhesion promoter and encapsulant. As the demand for advanced IC packaging continues to grow, we expect that this work will provide a base understanding of the possibilities of wholistic AM design and fabrication.   

First-ever measurement of hole velocity vs. electric field in polarization-induced two-dimensional hole gases in GaN/AlN heterojunctions

We present the first-ever measurements of the velocity vs. electric field (v-E) characteristic for a polarization-induced two-dimensional hole gas (2DHG) in undoped gallium nitride (GaN) on metal-polar aluminum nitride (AlN) heterostructures. The v-E characteristic provides an essential benchmark of carrier transport in low-field (mobility) and high-field (saturation) regimes and places an intrinsic limit on tenable RF device performance. Our sample, grown by molecular beam epitaxy, has a high-density 2DHG at the GaN/AlN interface degenerately occupying both the heavy- and light-hole valence bands with densities of 3.1×10¹³/cm² and 0.4×10¹³/cm², respectively, as determined with magneto-transport measurements fit to a 2-carrier model. We measure v-E from 4.2 to 300K with a pulsed voltage input and two-point current and voltage (IV) measurement of a test structure with an etched constriction of micron-scale dimensions. The ensemble hole velocity and average electric field in the constriction are calculated from the measured IV, hole density, and constriction dimensions. We observe ensemble saturation velocities of 3.4×10⁶ cm/s at 4.2 K and 2.5×10⁶ cm/s at 300 K, 2-3x slower than previous photo-assisted measurements in undoped bulk GaN with four orders lower equivalent hole density.   

Injection of spin-polarized electrons from ferromagnetic Fe3O4 nanoparticles into CdSe/CdZnS colloidal nanoplatelets

We have studied the magnetic field dependence of the electroluminescence (EL) from organic light emitting devices (LEDs).  The LEDs incorporate a layer of CdSe/CdZnS core/shell colloidal quantum wells also known as nanoplatelets as the electron-hole recombination site.  The injected electrons transport through a layer of ferromagnetic Fe₃O₄nanoparticles and thus become spin polarized predominantly in their -1/2 spin state before they are captured by the nanoplatelets.  The  emitted EL is circularly polarized as σ₊ (LCP) and shows hysteretic behavior with maximum circular polarization of 4 % , coersive field of 0.16 tesla, and remanent polarization of 1 %.  The polarization from a reference device that does not incorporate the Fe₃O₄ nanoparticle layer does not exhibit hysteresis.  We interpret the observed results as due to the fact that the injected electrons become spin-polarized as they transport through the Fe₃O₄nanoparticle layer.   The hysteresis disappears for T > 100 K.     

Anisotropic Materials for Additive Packaging Solutions: Anisotropic Ink for Flexible and Conformal Circuits.

As demands for additively manufactured circuits increase, there exists an ever-growing demand for flexible circuits and circuits on non-traditional substrates. This work presents the effects of a commercial off the shelf anisotropic ink (Creative Materials 124-19A) on advanced packaging solutions related to printed, conformal, and flexible RF electronics. This abstract analyzes the effects of anisotropic ink to simplify the manufacturing process by creating customized vertical pathways for electrical connections. Specifically, we analyze reliability, conductivity, loss, cross-coupling, and adhesion for surface mount components ranging from discrete passive electronics to high frequency packaged RF components. These results include long term bend testing, electrical testing, and temperature cycling. We will describe methods to successfully utilize anisotropic material systems in ways that will decrease pick-and-place alignment tolerances, improve reliability, and enable free form integration with customized structures and interposers.   

Advancing Semiconducting Polymer Patterning: Photothermal Approach for Sub-Micron Feature Fabrication for Electronic photodetector

 The industrial development of Semiconducting Polymers (SPs) faces a significant hurdle in the absence of an inexpensive, rapid, and viable patterning technology capable of producing sub-micron features. In this study, we explore Photothermal Patterning as a promising technique that leverages the solubility characteristics of SPs to address this challenge. The Photothermal Patterning process involves exposing an SP film to a semi-poor solvent mixture, rendering the polymer insoluble at room temperature. Subsequently, the SP film is exposed to laser radiation at a wavelength that is strongly absorbed by the SP in its solid state. The absorption of photons leads to localized heating, causing the SP to dissolve once the temperature surpasses its dissolution threshold, resulting in the formation of negative patterns. To validate the feasibility of this approach, we conducted experiments using the Alvéole PRIMO, a commercially available cleanroom equipment. Additionally, we developed a quasi-steady state model to investigate the dissolution behavior of SPs in solvent mixtures induced by a Gaussian laser beam's heating effect. Through our analysis, we successfully determined the depth and width of the patterns obtained and identified the influence of solubility kinetics on heat transfer dynamics. By gaining a comprehensive understanding of the heat transfer effects, we have been able to identify the regime in which these effects dominate, thereby enabling us to modify the shape of the patterns obtained. Leveraging this knowledge, we aim to employ the Photothermal Patterning technique to fabricate P3HT patterns over gold electrodes, with the goal of obtaining a functional NIR photodetector. This research significantly contributes to the development of a cost-effective and rapid patterning technology for SPs, opening up new possibilities for their industrial applications in the field of electronic devices.   

Poly(dimethylsiloxane)-Incorporated Block Copolymer-Typed Donor for High Performance and Stretchable Solar Cell

High efficiency and superior stretchability are the dual key factors of polymer solar cells (PSCs) for an energy supplier of wearable devices. The popular polymer donors (PDs) and small molecule acceptors (SMAs) comprising an active layer of PSC exhibit rigid structures for higher optoelectrical properties but simultaneously show inferior mechanical robustness. In this regard, block copolymer (BCP) consisting of conjugated PD block and flexible elastomer block can address this inferior stretchability by utilizing the stretchability of flexible elastomer without phase separation between the elastomer and other components. Thus, we designed PD (PM6)-b-Poly(dimethylsiloxane) (PDMS)-typed tri-BCP as the PD to realize highly efficient and stretchable PSCs. Additionally, PM6-b-PDMS with different PDMS blocks were further compared. We find that PM6-b-PDMS typed tri-BCP showed higher efficiency (> 17.5%) and 12-fold higher mechanical robustness (toughness of PM6-PDMS19:L8-BO= 5.60 MJ m−3) compared to the reference PM6:L8-BO blend films (toughness= 0.45 MJ m−3). Interestingly, PM6:L8-BO:PDMS ternary blend showed much lower efficiency (4.13%) and mechanical robustness (0.07 MJ m−3) than the previous two blends. This study implies the importance of the utilization of elastomers by the tri-BCP method to realize high-performance and mechanically robust PSCs.   

Comparing resonant cavity and on-wafer measurements of the complex permittivity of fused silica to 110 GHz

Researchers rely on resonant cavity and on-wafer measurements of complex permittivity for millimeter-wave circuit design and simulations. Resonant cavity measurements are more accurate but only measure discrete (often single) frequencies. On-wafer measurements are less accurate but offer broadband measurements over huge frequency ranges. Here, we compare resonant cavity and on-wafer complex permittivity measurements of the same fused silica wafer. We quantify the uncertainty of each method and the agreement between methods. Careful wafer design lets us cut coupons for resonant cavity measurements and chips for on-wafer measurements from a single wafer. Comparing and correlating these measurements gives us broadband complex permittivity (on-wafer) anchored with much smaller uncertainties at discrete frequencies (resonant cavities). In addition to the frequency-dependent properties of fused silica, this study provides insight into the overall measurement science surrounding millimeter-wave materials.   

Free-Form RF Sensing: Multifunctional, Multilayer Microwave Design on Doubly-Curved Fiberglass Laminates

Additive manufacturing has revolutionized traditional manufacturing processes, allowing for novel functionalities and unique form-factors within existing systems. Oftentimes, it is desirable to integrate electrical and/or communication technology into an existing part without disturbing its existing structural properties- such a process becomes especially challenging on surfaces with large curvatures or surfaces internal to an existing part. In this work, we utilize a novel multilayer insert-based approach to integrate an RF sensing circuit directly within an electrical glass (E-glass) ogive nose cone. These inserts enable detection of X-band frequency signals, utilizing a fully aerosol jet-printed ground plane, antenna, and transmission lines, alongside discrete amplifiers, envelope detectors, and capacitor networks. This work demonstrates and overcomes constraints imposed by the substrate's material properties such as impedance matching and loss.[MCJ1] Electromagnetic performance was verified both experimentally and utilizing Ansys HFSS simulations, and the impacts of curvature on circuit performance were analyzed. The resulting RF system demonstrates not only full functionality, but the potential for such techniques to be expanded towards the integration of microcontroller technology and various other sensors directly atop highly curved substrates.   

When Advanced Manufacturing Meets Machine Learning: A Study for Improved Printed RF Reliability

Additive manufacturing (AM) circuits and devices have primarily been focused on a low-count, high-customizability product space. Even though new AM technologies can successfully integrate radio frequency (RF) electronics on flexible and conformal substrates using AM technology, there are significant challenges when adapting this variable fabrication method with high-throughput manufacturing. However, with the advancement of image classification neural networks, there now exists a method to predictively analyze additively manufactured devices in-situ. This work integrates a convolutional neural network machine learning (ML) algorithm to predict the electrical and RF performance of a printed antenna structure (inverted-F) in the X-band. The antenna samples were fabricated using a Nordson EFD Pro4 micro pen dispensing printer and all simulations were performed using Ansys High Frequency Structure Simulator (HFSS). We utilized a novel ML training method using both simulation and experimental data sets for ML algorithm generation. Our algorithm has been able to generate accurate predictions of the RF performance with respect to antenna resonance frequency, resonance depth, and operational bandwidth. Additionally, the algorithm is capable of predicting new printed antenna designs using only simulated data sets. With the integration of this ML algorithm with in-situ process monitoring, we expect to usher in a new era of higher volume, and reliable, AM circuit production.   

Patterned polymer manufacturing by laser-ignited multi-initiation-point frontal polymerization

We present laser-patterned photothermal heating as a new means to simultaneously initiate self-propagating polymerization reactions at multiple locations in a 2-D sample. While frontal polymerization (FP) is well established for rapid polymerization of thermoset plastics using only a small point input of heat rather than a kiln, until now FP initiated at more than two points simultaneously has not been demonstrated. We incorporated carbon black (CB) particles into liquid resin (dicyclopentadiene; DCPD) to enhance absorption of energy from a rapidly scanned Ti:Sapph laser (800nm) focused on a shallow and broad sample (3 mm x 10 cm; d x w). We demonstrate successful multipoint polymerization at up to seven sites and in various geometries and show that initiation in DCPD+CB requires an approximately fixed energy input at high powers where thermal diffusion can be neglected. We also present a theoretical framework for predicting the seam patterns formed by the collision of multiple fronts, and an inverse solution for determining the initiation points required to form a desired material pattern. Future applications of this approach could be used for rapid, energy-efficient manufacturing of novel patterned materials with composite-like properties.   

Novel bioelectronic interface achieved by coupling an integrated circuit with bacterial-flagellar-motor-rotation

The bacterial flagellar motor is one of nature’s rare molecular machines. Its direction of rotation is regulated by the chemotactic network, which can sense down to nanomolar concentrations of specific chemicals on the time scale of seconds. The motor can thus serve as a biosensor with unprecedented speed and sensitivity. However, at the resolution needed motor speed and rotational direction are currently detected optically, using complex equipment. A step change in harnessing the sensing potential of the motor and associated signalling network is to detect its rotation electrically and with high throughput. Here we demonstrate such detection using a custom-designed integrated circuit (IC) with micron-sized electrodes.

Our bioelectronic transducer is based on a single bacterium with a rotating motor attached close to a set of micron-sized electrodes, which is then probed with a high-frequency voltage to measure the impedance change due to the rotating flagella. The frequency of impedance changes we obtain coincides with the speed of rotation seen optically. To assist the liquid delivery to the electrodes and the IC, whose area is roughly the size of mm², we use a two-layer microfluidics channel with customised geometry. The technology has the potential to revolutionise whole-cell biosensors and their application, because it offers electrical readout, while at the same time bioengineering of whole cells promises to significantly expedite the redesign for sensing of novel analytes.