Hemispherical Silicon Research Articles

A CMOS High-Power Broadband 260-GHz Radiator Array for Spectroscopy

A high-power broadband 260-GHz radiation source using 65-nm bulk CMOS technology is reported. The source is an array of eight harmonic oscillators with mutual coupling through four 130-GHz quadrature oscillators. Based on a novel self-feeding structure, the harmonic oscillator simultaneously achieves the optimum conditions for the fundamental oscillation and the 2nd-harmonic generation. The signals at 260 GHz radiate through eight on-chip slot antennas, and are in-phase combined inside a hemispheric silicon lens attached at the backside of the chip. Similar to the laser pulse-driven photoconductive emitter in many THz spectrometers, the radiation of this source can also be modulated by narrow pulses generated on chip, which achieves broad radiation bandwidth. Without modulation, the chip achieves a measured continuous-wave radiated power of 1.1 mW, and an EIRP of 15.7 dBm. Under modulation, the measured bandwidth of the source is 24.7 GHz. This radiator array consumes 0.8-W DC power from a 1.2-V supply.

Silicon Micromachined Lens Antenna for THz Integrated Heterodyne Arrays

In this paper, we present the design, fabrication, and measurements of a lens THz antenna that can be fabricated using conventional photolithography and deep reactive etching processes. The antenna is composed of an extended hemispherical silicon lens and a leaky wave waveguide feed. Both elements are fabricated using silicon micromachining techniques, enabling the fabrication of future large antenna arrays with a parallel process. To show the concept, a first antenna prototype has been fabricated using this fabrication process. Measurements obtained at 550 GHz are presented.

Characterization of Metal-Semiconductor Schottky Diodes and Application on THz Detection

This paper presents a kind of air-bridged GaAs Schottky diodes which offer ultra low parasitic capacitance and series resistance in millimeter and THz wavelength. The Schottky barrier diodes have several advantages when used as millimeter wave and terahertz video, or power detectors. These include their fast time response, room temperature operation, simple structure and low cost. This paper describes the characterization of the metal-semiconductor Schottky diodes including principle, diode structure, non-linear voltage-current characteristic and signal-rectifying performance. For application, a quasi-optical THz detector was made by using the proposed Schottky diodes. It utilized a hyper hemispherical silicon lens to coupleand THz radiation to the diodes by integrating on a broadband planar bow-tie antenna. The measurement results of the Schottky diode based detector show a good room temperature performance.

Beam Pattern Measurements of Millimeter-Wave Kinetic Inductance Detector Camera With Direct Machined Silicon Lens Array

We have developed 220 and 440-GHz cameras using microwave kinetic inductance detectors (MKIDs) for astronomical observations. The optical system of the MKID camera is based on double-slot antennas and extended hemispherical silicon lens arrays. The lens diameter is three times the target wavelength. The 220-GHz camera and the 440-GHz camera have 9 pixels and 102 pixels, respectively. The silicon lens array has been directly machined using a high-speed spindle on an ultra-precision machine. The shape fabrication error and the surface roughness of the top of the lens were typically less than 10 μm (peak-to-valley) and about 0.7 μm (rms), respectively. The beam patterns of the MKID camera were measured and are in good agreement with the calculations.

Design Guidelines for a Terahertz Silicon Micro-Lens Antenna

A silicon lens antenna suited for future integrated terahertz arrays has been proposed recently. The antenna consists of an extended hemispherical silicon lens fed by a leaky-wave waveguide feed. The primary advantage is that the antenna is compatible with silicon micro-fabrication techniques as only a small sector of the lens is actually used. Moreover, it can be easily integrated with other silicon micromachined front-end components. In this letter, the design and optimization details of such a micro-lens antenna is presented. The design is validated with a set of measurements at 550 GHz from a prototype that has been fabricated using laser micro-fabrication.

Studying integrated silicon-lens antennas for radio communication systems operated in the 60 GHz frequency band

We consider the development of an integrated lens antenna for LAN radio communication systems operated in the 60 GHz frequency band. The antenna is an extended hemispherical silicon lens. On its flat surface, a microstrip antenna element is located. The use of silicon, which has a dielectric permittivity e = 11.7, as the lens material ensures the maximum range of scanning angles for the minimum axial size of the lens. The approximate analytical formulas, which are used for initial calculations of the lens parameters, allow one to evaluate the basic parameters of the lens antenna integrated with the microstrip antenna element. For further optimizing the parameters of the lens and the antenna element, 3D simulation of the electromagnetic-field distribution was performed. Based on its results, we have developed and manufactured extended hemispherical silicon lenses, which had radii of 6 and 12 mm. The planar microstrip antenna element was manufactured by the low temperature co-fired ceramics (LTCC) technology. The results of simulation and experimental studies of the manufactured prototypes demonstrate that the developed lens antennas has directivities of 17.6 and 23.1 dBi for lenses with radii of 6 and 12 mm, respectively. In this case, the maximum beam deflection angle is achieved, which is equal to 55°, while the permissible decrease in the directivity is no more than 6 dBi compared with the case of a non-deflected beam. The obtained results show that the developed integrated lens antennas can find applications in high-speed radio communication systems operated in the millimeter-wave range.

Numerical investigation of magnetic field effect on pressure in cylindrical and hemispherical silicon CZ crystal growth

AbstractThe effect of axial magnetic field of different intensities on pressure in silicon Czochralski crystal growth is investigated in cylindrical and hemispherical geometries with rotating crystal and crucible and thermocapillary convection. As one important thermodynamic variable, the pressure is found to be more sensitive than temperature to magnetic field with strong dependence upon the vorticity field. The pressure at the triple point is proposed as a convenient parameter to control the homogeneity of the grown crystal. With a gradual increase of the magnetic field intensity the convection effect can be reduced without thermal fluctuations in the silicon melt. An evaluation of the magnetic interaction parameter critical value corresponding to flow, pressure and temperature homogenization leads to the important result that a relatively low axial magnetic field is required for the spherical system comparatively to the cylindrical one.

Dual-Polarized Sinuous Antennas on Extended Hemispherical Silicon Lenses

This paper examines the performance of dual-linear sinuous antennas on silicon extended hemispherical silicon dielectric lenses. A theoretical impedance of 106 Ω is identified based on the analysis of an ideal self-complementary structure, and this result compares well with simulations and measurements. The radiation properties of a linearly polarized sinuous antenna are simulated using Method of Moments software coupled to a GO/PO code, and also agree well with measurements. The results indicate that the sinuous antenna is an excellent wideband planar feed for a silicon lens, with cross-polarization levels below -17 dB, and polarization variations of ±5° over two octaves in frequency. The application areas are millimeter-wave, wideband, dual-polarized radio-astronomy receivers.

A 15–50-GHz Quasi-Optical Scalar Network Analyzer Scalable to Terahertz Frequencies

A 15-50-GHz two-port quasi-optical scalar network analyzer consisting of a transmitter and receiver built in a planar technology is presented. The network analyzer is based on a Schottky-diode multiplier and mixer integrated inside a planar antenna and fed differentially by a coplanar waveguide transmission line. The antenna is placed on an extended hemispherical high-resistivity silicon substrate lens. The local oscillator signal is swept from 3 to 5 GHz and high-order harmonic mixing in both the up- and down-conversion mode is used to realize the RF bandwidth. The network analyzer has a dynamic range of >;50 dB in a 1-kHz bandwidth, and was successfully used to measure frequency-selective surfaces with <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">f</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> =20, 30, and 40 GHz and a second-order bandpass response. Furthermore, the system was built with circuits and components for easy scaling to millimeter-wave frequencies, which is the primary motivation for this work.

Sharp silicon tips with different aspect ratios in wet etching/DRIE and surfactant-modified TMAH etching

A simple, high yield method of surfactant-modified wet anisotropic etching for the fabrication of sharp silicon tips is proposed in the applications of scanning probe microscope (SPM) and vacuum microelectronics. The formation of this new tip has been explained as the change in the local etch rate brought about by the strong adsorption of surfactant molecules in the apex of a silicon tip. In order to understand this point, the different etch rates of the same orientations tested on the hemispherical silicon (with curvature) and flat samples (no curvature) are investigated, and the adsorption thicknesses (or densities) of surfactants on various silicon surfaces measured by an ellipsometer are obtained. Tips with different aspect ratios (0.8:1 and 6:1) have been successfully fabricated on silicon (100) and (111) by the combination of etching in pure tetramethylammonium hydroxide (TMAH) or deep reactive ion etching (DRIE) and etching in surfactant-modified TMAH solutions, having the advantages of good uniformities, low temperatures, low costs and complementary metal oxide semiconductor (CMOS)-compatible. The apex of each resultant tip after the treatment in surfactant-added wet etchants typically can have a radius of curvature of 4–5nm on silicon (100) or even ≤2nm on silicon (111) without any subsequent oxide sharpening process.

Integrated 585-GHz Hot-Electron Mixer Focal-Plane Arrays Based on Annular Slot Antennas for Imaging Applications

We have developed 585-GHz quasi-optical mixers and focal-plane arrays (FPAs) comprised of planar annular slot antennas (ASAs) with integrated niobium hot-electron bolometers for imaging applications. In order to optimize the single-element mixer design, the embedding impedance of the single ASA presented to the bolometer is analyzed using the induced electromotive force (EMF) method by including the antenna feed contribution. This approach has been further expanded to analyze the ASA self-impedance and mutual impedance in an array by utilizing the even-odd mode analysis. In addition, the far-field radiation patterns of the ASAs mounted to an extended hemispherical high-resistivity silicon lens have been calculated using the ray-tracing techniques. The details of circuit design and fabrication are presented in this study. Single mixer element measurement results have shown that a conversion gain of -11.9 dB and a double-sideband (DSB) receiver noise temperature of ~650 K have been achieved. Initial array imaging experiment results are presented and show excellent agreement with theory and simulation data. A spatial resolution of ~2.75 mm has been demonstrated at 585 GHz for a 1-D mixer FPA that is capable of diffraction-limited imaging. <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Y</i> -factor measurements show DSB mixer noise temperatures of 1675 and 3517 K with mixer conversion gains of -14.73 and -17.74 dB, respectively, have been obtained for two adjacent elements in a mixer array, which is comparable to the results reported in the literature.

Terahertz and Millimetre Wave Imaging with a Broadband Josephson Detector Working above 77 K

A high-Tc superconducting (HTS) broadband Josephson detector has been developed and applied to millimetre wave (mm-wave) and terahertz (THz) imaging. The detector is based on a YBa2Cu3O7-x (YBCO) step-edge Josephson junction, which is coupled to a thin-film log-periodic antenna, designed for operation at 200–600 GHz, and a hemispheric silicon lens. The junction parameters have been optimised to achieve a high IcRn value so that the detector responds well to the specified frequencies at liquid nitrogen temperature (77 K). Images at ∼200 GHz and ∼600 GHz were acquired with the same detector; each demonstrated their unique properties. The results demonstrate the potential of achieving a cheaper, compact and portable multi-spectral imager based on a HTS detector.

A phenomenological model of polishing of silicon with diamond abrasive

A phenomenological model of polishing hemispherical silicon asperities with spherical diamond abrasives is presented. Removal of the asperity material is quantitatively determined by a removal rate constant K. It is based on our molecular dynamics (MD) simulation studies considering the probability of removal of asperity atoms by an abrasive. The dependence of the removal rate constant K on the diameter and velocity of abrasives, number of asperities and abrasives per unit area, and cutting depth has been investigated. The rate constant K is found to be insensitive to the density of asperities, but linearly dependent on the density of abrasives.

Ordered amorphous silicon nanoisland arrays and reflection spectral dependence on nanoisland geometrical parameters

We report an anodic porous alumina mask technique for fabricating orderly hemispherical silicon nanoisland arrays with island diameters of 30–120 nm. Reflection spectral measurements show that the phase transition of incident light can periodically be transferred with changes in geometrical parameters of the ordered arrays. Thus the redshift of the reflection peak with decreasing both sizes of the nanoislands and incident angle of light wave can be explained well on the basis of a modified rigorous vector coupled-wave theory. The simple fabrication technique and reflection spectral redshift of the ordered arrays have potential applications in optical devices and solar cells.

Infrared dipole-coupled bolometer response on a hemispherical silicon immersion lens

Response of an infrared ( λ = 10.6 μm) dipole antenna-coupled bolometer fabricated at the center of the flat side of a hemispherical silicon immersion lens is presented. Predicted and measured antenna patterns as well as the ratio of power from the lens-side to the air-side are provided as a function of illumination F/#. The power-division ratio, Φ lens / Φ air , is shown to be given by the square root of the lens dielectric constant, ϵ Si 1 / 2 = 3.4 , for F/# larger than F/2 whereas as F/# decreases to F/1 the ratio increases to 5 due to off-axis features in the radiation pattern.

Anisotropy of photocurrent for two-photon absorption photodetector made of hemispherical silicon with $(\overline{1}10)$ plane

We fabricated a hemispherical nearly-intrinsic Si-based photodetector with ( \(\bar{1}10)\) plane. The photocurrent generated from the detector under a continuous wave laser at the wavelength of 1.3 μm was observed. The photocurrent shows a quadratic dependence on the incident optical power. The dependence of the photocurrent on the azimuth of the incident optical field is consistent with the anisotropy of the two-photon absorption in Si crystals. The ratio of the two nonzero independent components of the third-order susceptibility of silicon is obtained to be 0.42 from the observed result of the anisotropy of the photocurrent.

Lock-in thermal IR imaging using a solid immersion lens

A hemispherical silicon solid immersion lens (SIL) was used to improve the spatial resolution of front-side thermal IR imaging in lock-in mode. The bottom of the SIL was cone-shaped to reduce the footprint of the SIL to the size of the imaged region. Caused by the lock-in operation mode, the detection limit improves by 2–3 orders of magnitude, and scattered light does not limit the image contrast. By using this SIL in combination with an IR camera working in the 3–5 μm wavelength range, a spatial resolution of 1.4 μm was obtained for thermal IR imaging. An automatic SIL positioning facility was constructed to place the SIL exactly in the center of the imaged region and to easily remove it after the detailed investigation.

Effect of magnesium in KOH solution on the anisotropic wet etching of silicon

Etching characteristics of single crystal silicon in KOH solution containing magnesium were investigated. Etch rate of silicon slightly decreases by the Mg of the order of 10 ppm in 32 wt.% KOH, while the etched surface roughness did not change. In order to evaluate the effects of ppm-level Mg in KOH solution for a number of crystallographic orientations, the etching experiment using a hemispherical single crystal silicon specimen was performed. The anisotropy of etch rate was almost the same as that without addition, and the etch rate decreased at almost all orientations with an addition of 26 ppm. The surface roughening caused by the ppb-level of Cu in KOH solution could be fully recovered by adding Mg of the order of 10 ppm in KOH solution.

Silicon lens-coupled bow-tie InGaAs-based broadband terahertz sensor operating at room temperature

A passive detection scheme for broadband, 10 GHz–2.52 THz, sensing at room temperature is demonstrated using a hemispherical silicon lens-coupled diode of an asymmetrically-shaped bow-tie geometrical form. The device is fabricated from an MBE-grown In0.54Ga0.46As wafer as mesas of 3 µm depth produced by wet etching. The detector exhibits voltage sensitivity about 5 V/W below 1 THz.

Localization and physical analysis of dielectric weaknesses for state-of-the-art deep trench based DRAM products

Stressed deep trench capacitors of Dynamic Random Access Memories (DRAM) were analyzed regarding the localization within a test array. A preparation method to find the position within the failing trench and to give information for process improvements is reported. Differences between the dielectrics nitride/oxide and aluminumoxide were seen. The investigations were done mostly for trench geometries of a 110nm technology. One first preparation was also successful for a 90nm technology with enlarged trench surfaces by hemispherical silicon grains ( HSG ).