Planar Fabrication Technology Research Articles

Construction of All Multilayer Monolithic RSMTs and Its Application to Monolithic 3D IC Routing

Monolithic three-dimensional (M3D) integration allows ultra-thin silicon tier stacking in a single package. The high-density stacking is acquiring interest and is becoming more popular for smaller footprint areas, shorter wirelength, higher performance, and lower power consumption than the conventional planar fabrication technologies. The physical design of M3D integrated circuits requires several design steps, such as three-dimensional (3D) placement, 3D clock-tree synthesis, 3D routing, and 3D optimization. Among these, 3D routing is significantly time consuming due to countless routing blockages. Therefore, 3D routers proposed in the literature insert monolithic interlayer vias (MIVs) and perform tier-by-tier routing in two substeps. In this article, we propose an algorithm to build a routing topology database (DB) used to construct all multilayer monolithic rectilinear Steiner minimum trees on the 3D Hanan grid. To demonstrate the effectiveness of the DB in various applications, we use the DB to construct timing-driven 3D routing topologies and perform congestion-aware global routing on 3D designs. We anticipate that the algorithm and the DB will help 3D routers reduce the runtime of the MIV insertion step and improve the quality of the 3D routing.

Inverse design strategies for buckling-guided assembly of 3D surfaces based on topology optimization

Complex three-dimensional (3D) mesostructures in advanced functional materials are attracting increasing interest, due to their widespread applications. Mechanically-guided 3D assembly through compressive buckling provides deterministic routes to a rich diversity of 3D mesostructures and microelectronic devices, with feature sizes ranging from sub-microscale to millimeter-scale. Existing studies established inverse design methods that map the target 3D geometry onto an unknown 2D precursor, but mainly focusing on filamentary ribbon-type geometries. Although strategies relying on spatial thickness variation of 2D precursors have been reported to achieve inverse design of 3D surfaces, this could lead to a lack of compatibility with well-developed planar fabrication technologies. In the framework of buckling-guided 3D assembly, this paper presents a computational method based on topology optimization to solve the inverse design problem of 3D surfaces from 2D precursors with uniform thickness distributions. Specifically, curvy ribbon components were exploited to discretize nondevelopable target surfaces, and then optimized to ensure that the assembled 3D surface has the best match with the target geometry. Combined computational and experimental studies over a dozen of elaborate examples, encompassing both the caged and even general target surfaces, demonstrate the effectiveness and applicability of the proposed method.

Millimeter Wave Multi-Port Interferometric Radar Sensors: Evolution of Fabrication and Characterization Technologies.

Recent advances in millimeter wave technologies, both in component and system design, in line with important size and cost reductions, have opened up new applications in ultra-high-speed wireless communications, radar and imaging sensors. The paper presents the evolution of millimeter wave circuit and modules fabrication and characterization technologies in the past decades. Novel planar low-cost fabrication technologies have been successfully developed in this period. In combination with the standard rectangular wave-guide technology, these offer great opportunities for prototyping and testing of future millimeter wave transceivers or front-ends, which integrate antenna arrays, down-converters, modulators, amplifiers, etc., in a compact fixture. The paper uses, as a suggestive example, the evolution of the multi-port interferometric front-ends implementation from millimeter wave bulky components and systems to miniaturized and high-efficient ones. Circuit and system designs are carefully done to avoid (as much as possible) complicated calibration methods or difficult post-processing of baseband data. This requires an increased effort in design and fabrication, but it allows miniaturization, low-power consumption, while keeping very good overall performances. Useful and straightforward laboratory characterization techniques of circuits and systems are described in detail.

Excitation of graphene surface plasmons polaritons by guided-mode resonances with high efficiency.

An Otto-like configuration for the excitation of graphene surface plasmon polaritons (GSPPs) is proposed. The configuration is composed of a metallic grating-dielectric-waveguide structure and a monolayer graphene with a subwavelength vacuum gap between them. The evanescent field located at the bottom surface of the dielectric waveguide corresponding to grating-coupled guided-mode resonances (GMRs) is utilized to efficiently excite the highly confined GSPPs. The finite difference time domain method is used to investigate the behaviors of the GMR-GSPP hybrid modes. The dispersion relations of GMRs and GSPPs are calculated and the numerical results further identify the excitation of GMR-GSPP hybrid modes. By changing the gap between the graphene layer and the bottom of the dielectric waveguide and the Fermi energy of graphene, the resonant frequencies of GMR-GSPP hybrid modes can be continuously tuned. When the optimized excitation condition is satisfied, the maximum energy enhancement factor in the gap can reach about 500 at the resonant frequencies. The proposed structure can be used to realize highly sensitive, compatible with planar fabrication technology, and electrically (mechanically) tunable sensors.

A novel capacitive sensing structure for simultaneous detection of biaxial low-g acceleration in a commercial MEMS process

The authors report a novel MEMS capacitive sensing structure that utilizes a single-layer electroplated gold to achieve simultaneous sensing of biaxial acceleration with low cross-axis sensitivity. The capacitive sensing structure is designed for the in-plane biaxial accelerometer with high frequency ratio and low-g acceleration range. The etching precision of the large proof-mass suspension is guaranteed by the design of detachable supporting islands. Then, different locations are explored in arranging the capacitors, for which the corresponding estimation algorithms are derived. Finally, the proposed structure was fabricated under the commercial MicraGEM-Si platform based on silicon-on-insulator (SOI) technologies. In summary, the structural and fabrication designs of the MEMS capacitive sensing structure solve the problems in biaxial independent sensing, while offering: 3D connectivity of electrodes using planar fabrication technologies; large proof-mass fabrication precision; identical mobility range in all in-plane directions; and sensing algorithms for any regular polygonal shape.

Miniaturisation design of patch antenna using a low‐profile mushroom type meta‐substrate tailored with high permittivity

A new and simple method is proposed for the miniaturisation design of patch antenna utilising a low-profile mushroom type meta-substrate. The functional mushroom element is analytically studied. A simple designing rule is obtained to tailor the effective high permittivity for the element as one desires. In validation, one proof of the conceptual patch antenna is presented experimentally loaded with the mushroom meta-substrate. The antenna size is 0.18λ0 × 0.18λ0 × 0.029λ0. Numerical and measured antenna characteristics are in good agreement. The impedance is well matched in bandwidth of 2.1%. The measured cross-polar levels are all below −23 dB. The measured antenna gain is 5.7 dBi and the radiation efficiency is 85%. The authors remark that the meta-substrate is intrinsically compatible with printed planar fabrication technology and can be easily made using common dielectrics and metals of low cost. The designing method in this work is simple and yet promising. With the intuitive analytical rule, any other desirable high index permittivity can be further obtained for future potential compact patch antenna designs.

Numerical studies on a plasmonic temperature nanosensor based on a metal-insulator-metal ring resonator structure for optical integrated circuit applications

A nanosensor, based on a metal-insulator-metal (MIM) plasmonic ring resonator, is proposed for potential on-chip temperature sensing and its performance is evaluated numerically. The sensor components can be fabricated by using planar processes on a silicon substrate, making its manufacturing compatible to planar electronic fabrication technology. The sensor, constructed using silver as the metal rings and a thermo-optic liquid ethanol film between the metal layers, is capable of sensing temperature with outstanding optical sensitivity, as high as −0.53nm/°C. The resonance wavelength is found to be highly sensitive to the refractive index of the liquid dielectric film. The resonance peak can be tuned according to the requirement of intended application by changing the radii of the ring resonator geometries in the design phase. The compact size, planar and silicon-based design, and very high resolutions- these characteristics are expected to make this sensor technology a preferred choice for lab-on-a-chip applications, as compared to other contemporary sensors.

Photonic crystals possessing multiple Weyl points and the experimental observation of robust surface states.

Weyl points, as monopoles of Berry curvature in momentum space, have captured much attention recently in various branches of physics. Realizing topological materials that exhibit such nodal points is challenging and indeed, Weyl points have been found experimentally in transition metal arsenide and phosphide and gyroid photonic crystal whose structure is complex. If realizing even the simplest type of single Weyl nodes with a topological charge of 1 is difficult, then making a real crystal carrying higher topological charges may seem more challenging. Here we design, and fabricate using planar fabrication technology, a photonic crystal possessing single Weyl points (including type-II nodes) and multiple Weyl points with topological charges of 2 and 3. We characterize this photonic crystal and find nontrivial 2D bulk band gaps for a fixed kz and the associated surface modes. The robustness of these surface states against kz-preserving scattering is experimentally observed for the first time.

Design, fabrication and characterization of multi-guard-ring furnished [formula omitted] silicon strip detectors for future HEP experiments

Si detectors, in various configurations (strips and pixels), have been playing a key role in High Energy Physics (HEP) experiments due to their excellent vertexing and high precision tracking information. In future HEP experiments like upgrade of the Compact Muon Solenoid experiment (CMS) at the Large Hadron Collider (LHC), CERN and the proposed International Linear Collider (ILC), the Si tracking detectors will be operated in a very harsh radiation environment, which leads to both surface and bulk damage in Si detectors which in turn changes their electrical properties, i.e. change in the full depletion voltage, increase in the leakage current and decrease in the charge collection efficiency. In order to achieve the long term durability of Si-detectors in future HEP experiments, it is required to operate these detectors at very high reverse biases, beyond the full depletion voltage, thus requiring higher detector breakdown voltage. Delhi University (DU) is involved in the design, fabrication and characterization of multi-guard-ring furnished ac-coupled, single sided, p+n−n+ Si strip detectors for future HEP experiments. The design has been optimized using a two-dimensional numerical device simulation program (TCAD-Silvaco). The Si strip detectors are fabricated with eight-layers mask process using the planar fabrication technology by Bharat Electronic Lab (BEL), India. Further an electrical characterization set-up is established at DU to ensure the quality performance of fabricated Si strip detectors and test structures. In this work measurement results on non irradiated Si Strip detectors and test structures with multi-guard-rings using Current Voltage (IV) and Capacitance Voltage (CV) characterization set-ups are discussed. The effect of various design parameters, for example guard-ring spacing, number of guard-rings and metal overhang on breakdown voltage of test structures have been studied.

Shape-dependent light scattering properties of subwavelength silicon nanoblocks.

We explore the shape-dependent light scattering properties of silicon (Si) nanoblocks and their physical origin. These high-refractive-index nanostructures are easily fabricated using planar fabrication technologies and support strong, leaky-mode resonances that enable light manipulation beyond the optical diffraction limit. Dark-field microscopy and a numerical modal analysis show that the nanoblocks can be viewed as truncated Si waveguides, and the waveguide dispersion strongly controls the resonant properties. This explains why the lowest-order transverse magnetic (TM01) mode resonance can be widely tuned over the entire visible wavelength range depending on the nanoblock length, whereas the wavelength-scale TM11 mode resonance does not change greatly. For sufficiently short lengths, the TM01 and TM11 modes can be made to spectrally overlap, and a substantial scattering efficiency, which is defined as the ratio of the scattering cross section to the physical cross section of the nanoblock, of ∼9.95, approaching the theoretical lowest-order single-channel scattering limit, is achievable. Control over the subwavelength-scale leaky-mode resonance allows Si nanoblocks to generate vivid structural color, manipulate forward and backward scattering, and act as excellent photonic artificial atoms for metasurfaces.

Hybrid 2D–3D optical devices for integrated optics by direct laser writing

Integrated optical chips have already been established for application in optical communication. They also offer interesting future perspectives for integrated quantum optics on a chip. At present, however, they are mostly fabricated using essentially planar fabrication approaches like electron-beam lithography or UV optical lithography. Many further design options would arise if one had complete fabrication freedom in regard to the third dimension normal to the chip without having to give up the virtues and the know-how of existing planar fabrication technologies. As a step in this direction, we here use three-dimensional dip-in direct-laser-writing optical lithography to fabricate three-dimensional polymeric functional devices on pre-fabricated planar optical chips containing Si3N4 waveguides as well as grating couplers made by standard electron-beam lithography. The first example is a polymeric dielectric rectangular-shaped waveguide which is connected to Si3N4 waveguides and that is adiabatically twisted along its axis to achieve geometrical rotation of linear polarization on the chip. The rotator’s broadband performance at around 1550 nm wavelength is verified by polarization-dependent grating couplers. Such polarization rotation on the optical chip cannot easily be achieved by other means. The second example is a whispering-gallery-mode optical resonator connected to Si3N4 waveguides on the chip via polymeric waveguides. By mechanically connecting the latter to the disk, we can control the coupling to the resonator and, at the same time, guarantee mechanical stability of the three-dimensional architecture on the chip. Direct laser writing is a popular scheme for constructing three-dimensional integrated optical structures. Martin Schumann and co-workers from the Karlsruhe Institute of Technology and the Institute of Nanotechnology in Germany used two-photon polymerization to create three-dimensional polymer objects such as bridge waveguides, a twisted-waveguide polarization rotator and free-standing disk resonators. The structures, which would be difficult or impossible to construct using planar lithography, were successfully integrated with silicon optical chips featuring silicon nitride waveguides that guide light in the 1,550 nm telecommunications wavelength window. The researchers say that their approach could also be used to provide convenient access to three-dimensional photonic crystals. An advanced form of this approach that exploits higher resolutions would allow the construction of structures that are compatible with visible wavelengths.

An all-polymer airflow sensor using a piezoresistive composite elastomer

This paper presents an all-polymer flexible micromachined flow sensor using acarbon-black based conductive composite elastomer as a piezoresistor. The device iscomposed of an out-of-plane curved flow sensing element formed using a polyimidefilm. The conductive composite elastomer combines a low Young’s modulus (∼1.72 MPa) and a high piezoresistive gage factor (∼7.3), making it an ideal material for the sensing application. Moreover, the use of thepolyimide film, which can be easily laser micromachined, as the material for devicefabrication enables the use of planar micromachining techniques, which minimizes processcomplexities. The proposed fabrication sequence combines the benefits of the polymericmaterials used, while simultaneously enabling a backside interconnect scheme for anarray of devices, without additional processing steps. The backside interconnectscheme allows for flow field mapping with minimum interference due to the sensingcircuitry. Individual sensors as small as 1.5 mm in length and 0.4 mm in width, with70 µm wideand 20–50 µm thick piezoresistor lines, have been fabricated. Wind tunnel testing demonstrated sensitivities as highas 66Ω/(m s−1). The integration of polyimide films and conductive elastomers into a flow sensing deviceusing the simple planar fabrication technologies discussed is suitable for reduced cost, largearea sensor array development, and can also leverage traditional flexible circuit fabrication.

Silicon photonic circuit with polarization diversity

We devised a silicon photonic circuit with polarization diversity that consists of polarization splitters and polarization rotators. The splitter is based on a simple directional coupler and the rotator has an off-axis double-core structure. Both devices can be made by using planar fabrication technology and require no complex proceses for the fabrication of three-dimensional structures. We fabricated a polarization-independent wavelength filter based on Si wire waveguides as an application of the polarization diversity. The filter consists of the polarization splitters, the rotators, and a ring resonator. The polarization-dependent loss of the filter is about 1 dB. A 10-Gbps data transmission with scrambled polarization is demonstrated.

Polarization rotator based on silicon wire waveguides

We describe a polarization rotator based on an off-axis double-core structure consisting of a silicon wire waveguide and a silicon-oxinitride waveguide. The rotator can be made by planar fabrication technology and do not require complex processes, such as three-dimensional structure formation. A rotator with 35-microm long provides the polarization rotation angle of 72 degrees and the polarization extinction ratio of 11 dB with the excess loss of about 1 dB. Our polarization rotator represents a significant step towards accomplishing an optical circuit with polarization diversity based on silicon wire waveguides.

Device Isolation by Plasma Treatment for Planar Integration of Enhancement/Depletion-Mode AlGaN/GaN High Electron Mobility Transistors

We demonstrate a new planar fabrication technology for integrating enhancement/depletion (E/D) mode AlGaN/GaN high electron mobility transistors (HEMTs) using fluoride plasma treatment techniques. The CF4 plasma treatment is used in two separate steps to achieve two objectives: 1) active device isolation; and 2) threshold voltage control for the E-mode HEMT formation. Compared with the devices formed by standard mesa etching, the HEMTs by planar process have comparable DC characteristics, with no obvious difference in device isolation. By using the planar process, the E/D-mode HEMTs are integrated on the same chip, and a direct-coupled FET logic inverter and a 17-stage ring oscillator are fabricated. When the supply voltage is 4.5 V, the ring oscillator yields a frequency of 146 MHz, corresponding to a propagation delay of 201 ps/stage.

Characterization of edgeless detectors fabricated by dry etching process

This work presents results from a new type of edgeless detector, fabricated using an innovative approach to reduce the conventional width of the terminating structure of position sensitive detectors to the detector rim, still using standard planar fabrication technology. A current terminating ring is used to decouple the electrical behaviour of the surface from the sensitive volume within a few tens of micrometres. The detectors, fabricated using a dry etching process to cut the detector as closely as possible to the detector rim, have been illuminated using an infrared laser. The detectors have very high efficiency up to the insensitive area which is located about 25 μm from the detector edge. A detector irradiated with neutrons has also shown good charge collection and lower leakage currents in the current terminating rings compared to non-irradiated ones.

Final size planar edgeless silicon detectors for the TOTEM experiment

The TOTEM experiment will detect leading protons scattered in angles of microradians from the interaction point at the Large Hadron Collider. This will be achieved using detectors with a minimized dead area at the edge. The collaboration has developed an innovative structure at the detector edge reducing the conventional dead width to less than 100 microns, still using standard planar fabrication technology. In this new development, the current of the surface is decoupled from the sensitive volume current within a few tens of micrometers. The basic working principle is explained in this paper. Final size detectors have been produced using this approach. The current-voltage and current-temperature characteristics of the detectors were studied and the detectors were successfully tested in a coasting beam experiment.

InP double‐hetero bipolar transistor technology for 130 GHz clock speed

Indium Phosphide-based Hetero Bipolar Transistors (HBTs) have shown strong potential for mm-wave power electronics and mixed-mode applications beyond 100 GHz clock speed. We have developed a planar fabrication technology using all dry etched mesas, which scales to 0.25 µm emitter size. Devices show cut-off frequencies of f t = 380 GHz and f max = 380 GHz simultaneously (optimized for highest f max) or f t = 410 GHz and f max = 340 GHz (optimized for f t). As technology test vehicles, we have realized static-by-four divider circuits running at up to 130 GHz with a baseline epitaxial structure yielding f t = 330 GHz and f max = 300 GHz; Voltage-Controlled oscillators fabricated in the 380 GHz technology delivered power output of 0 dBm at 180 GHz. The possibility of reducing the extrinsic base-collector capacitance along with the device height by selective ion-implantation of the subcollector is explored. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Edgeless detectors fabricated by dry etching process

This work is based on an innovative approach to reduce the conventional width of the terminating structure of position sensitive detectors to less than 50 μm, still using standard planar fabrication technology. The objective of this new development is to decouple the electric behaviour of the surface from the sensitive volume within a few tens of micrometers. The main idea of this work is to use a dry etching process to cut the detector as close as possible to the current terminating structure with the only limitation of the photolithography process resolution. The dry etching process offers the advantage of low damage surface if compared to diamond saw cut or laser drilling and the possibility of being part of the standard microelectronics fabrication process. Furthermore, the pattern of the cut lines can be determined by the photolithography step. In this work we present the electrical measurements together with the technique used to reduce the insensitive area of a standard microstrip detector to only 25 μm.

Planar edgeless silicon detectors for the TOTEM experiment

Silicon detectors for the Roman Pots of the the large hadron collider TOTEM experiment aim for full sensitivity at the edge where a terminating structure is required for electrical stability. This work provides an innovative approach reducing the conventional width of the terminating structure to less than 100 /spl mu/m, still using standard planar fabrication technology. The objective of this new development is to decouple the electric behavior of the surface from the sensitive volume within a few tens of micrometers. The explanation of the basic principle of this new approach together with the experimental confirmation via electric measurements and beam test are presented in this paper, demonstrating that silicon detectors with this new terminating structure are fully operational and efficient to under 60 /spl mu/m from the die cut.