Fundamental Oscillation Research Articles

(Invited) Combining SiGe BiCMOS and InP Processing in an on-top of Chip Integration Approach

The research on millimeter-wave circuits is driven by applications such as radar imaging and wideband communications. For some applications SiGe hetero junction bipolar transistors (HBTs) are limited in output power, determined by the physical properties of silicon. For SiGe devices with transit frequencies of 180 GHz a breakdown voltage BVCEO of 2.0 V can be measured. The increase in breakdown voltage means always a decrease in transit frequency. On the other hand, silicon is the leading material of modern semiconductor technology. It offers a high level of integration density and yield. SiGe-HBT device speed has increased to hundreds of gigahertz, however limited in output power compared to III-V semiconductor devices. Thus, merging the qualities of both III-V and Si technology will enable a new class of high-performance ICs.Our approach combines a 3” InP-DHBT transferred-substrate process [1] with a SiGe-BiCMOS process [2]. At first, silicon and InP wafers are processed separately. The silicon wafer runs through the complete production process with front-end and back-end in a 0.25 µm BiCMOS process with a five metal layers aluminum/tungsten back-end using silicon dioxide as interlayer dielectric and an additional tungsten local interconnect. The back-end-process was specially adapted for the following wafer bond process by planarization of the topmost metal (TM2) level. The InP wafer has a semi-completed front-end and one metal level of gold and benzocyclobutene (BCB) as the dielectric. At this stage the front-to-front bond process is performed (see Fig. 1 a). The ground metallization (Gd) of the InP wafer is embedded in BCB to achieve a surface step height of less than 100 nm. Prior to wafer bonding both wafers are spin coated with BCB. After a BCB curing process the two wafers are aligned and bonded. After the bond process the InP substrate is etched by HCl to expose the InP-DHBT structures (see Fig. 1 a). The vias between the InP and SiGe-BiCMOS structures are formed by inductively coupled plasma (ICP) reactive ion etching (RIE) dry etching through the BCB using SF6. Then they are electrically connected using a gold electroplating process (see Fig. 1 b).To demonstrate the capabilities of the heterointegration scheme an integrated signal source at 164 GHz was designed and fabricated [3]. It is an example of the different combinations of BiCMOS and InP circuit building blocks. It is shown in Fig. 2. The source consists of a fundamental voltage-controlled oscillator (VCO) in BiCMOS technology (left side in Fig. 2) which is interconnected by an optimized high frequency via transition to a doubler-amplifier combination in InP technology (right side of Fig. 2).Recently, the influences of the wafer bonding and the finalization of the InP-DHBT process on SiGe devices were investigated. It was found that the impact on the BiCMOS devices is rather small. The forward Gummel plot of a SiGe-HBT before and after hetero integration is shown in Fig. 3. There is a slight increase of the base current at low emitter-base voltages caused by leakage currents due to electrostatic discharges in etching processes in the post bonding procedure. But these changes are marginal. Nevertheless, options to remove these effects are being discussed, such as moderate anneal sequences (the post-fabrication temperature is limited to below 250°C due to the presence of BCB) and modifications to the post-waferbonding plasma etch recipes.

An AlGaAs/GaAs‐based planar Gunn diode oscillator with a fundamental frequency operation of 120 GHz

ABSTRACTThis letter reports the highest fundamental oscillator operating frequency of 120 GHz for gallium arsenide (GaAs)‐based Gunn diode. The letter describes the design, fabrication, and test of the aluminum gallium arsenide (AlGaAs)/(GaAs) planar Gunn diode with an anode to cathode separation of 1 μm and channel width of 120 μm. The planar Gunn diode was designed with an integrated series inductor in coplanar waveguide format. The experimental results showed that the planar Gunn diode oscillated at a fundamental frequency of 120.47 GHz with an RF output power −9.14 dBm. This is highest fundamental frequency and power recorded for a GaAs‐based Gunn diode. © 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:2449–2451, 2014

Oscillations of compact stars evolving towards the point of gravitational instability

A significant portion of compact objects will collapse to form black holes, e.g., a proto-neutron star with mass larger than the maximum mass the equation of state (EOS) can support at zero temperature will eventually collapse upon neutrino cooling or other dissipative processes. We found that in the cooling process the fundamental oscillation frequency ω would first rise to a peak value shortly before it drops abruptly to zero at the instability point, quite independent of the specific choice of the EOS and cooling mechanism. The rapidity of the drop gives a clear signal that a gravitational collapse is imminent.

Nonlinear acoustic oscillations in swirling gas flows

A class of exact solution of the gasdynamics equations with the linear dependence of the velocity components on the coordinates and a functional arbitrariness in the density (entropy) distribution is constructed. Using this class the characteristics of acoustic oscillations occurring, when a swirling gas flow deviates from the steady cyclostrophic equilibrium regime, that is, the equilibrium between the pressure gradient and the centrifugal force, are studied. An expression for the fundamental oscillation frequency agreeing with the measurements is derived.

Millimeter-wave hetero-integrated sources in InP-on-BiCMOS technology

The paper presents millimeter-wave (mm-wave) signal sources using a hetero-integrated InP-on-BiCMOS semiconductor technology. Mm-wave signal sources feature fundamental frequency voltage-controlled oscillators (VCOs) in BiCMOS, which drive frequency multiplier–amplifier chains in transferred-substrate (TS) InP-DHBT technology, heterogeneously integrated on top of the BiCMOS wafer in a wafer-level bonding process. Both circuits are biased through a single set of bias pads and compact low-loss transitions from BiCMOS to InP circuits and vice versa have been developed, which allows seamless signal routing through both technologies exhibiting 0.5 dB insertion loss up to 200 GHz. One VCO operates at 82 GHz with a tuning range of 600 MHz and an output power of approximately 8 dBm. A frequency doubler combined with this VCO circuit delivers 0 dBm at 164 GHz and a frequency tripler with a similar VCO delivers −10 dBm at 246 GHz. Another hetero-integrated W-band doubler–amplifier circuit demonstrates 12.9 dBm saturated output power with 5.9 dB conversion gain at 96 GHz. A direct comparison of the TS InP-DHBT MMIC with either silicon or traditional AlN carrier substrates shows the favorable properties of the hetero-integrated process discussed here. The results demonstrate the feasibility of hetero-integrated circuits operating well above 100 GHz.

Fundamental Oscillation up to 1.42 THz in Resonant Tunneling Diodes by Optimized Collector Spacer Thickness

We report an increase in the oscillation frequency of terahertz oscillators using AlAs/InGaAs double-barrier resonant tunneling diodes (RTDs) by optimizing the collector spacer thickness. For high-frequency oscillation of RTDs, the electron delay time, which is composed of the dwell time in the resonance region and the transit time in the collector depletion region, must be reduced. Although the transit time is reduced by a thin collector spacer, the capacitance increases. Thus, an optimum thickness of collector spacer layer exists. In this report, we investigate the dependence of oscillation frequency on the collector spacer thickness. The RTDs were integrated with 20-μm-long slot antennas, and oscillations up to 1.1, 1.42, and 1.29 THz were obtained for spacer thicknesses of 25, 12, and 6 nm, respectively. The optimum spacer thickness for high-frequency oscillation was around 12 nm. The highest frequency in this experiment was 1.42 THz oscillation, with an output power of ~1 μW. We also extracted the electron velocity in the collector depletion region and the dwell time from the dependence of the delay time on the collector spacer thickness.

Intrinsic Localized Modes of Harmonic Oscillations in Pendulum Arrays Subjected to Horizontal Excitation

The behavior of intrinsic localized modes (ILMs) is investigated for an array with N pendula which are connected with each other by weak, linear springs when the array is subjected to horizontal, sinusoidal excitation. In the theoretical analysis, van der Pol's method is employed to determine the expressions for the frequency response curves for fundamental harmonic oscillations. In the numerical calculations, the frequency response curves are presented for N = 2 and 3 and compared with the results of the numerical simulations. Patterns of oscillations are classified according to the stable steady-state solutions of the response curves, and the patterns in which ILMs appear are discussed in detail. The influence of the connecting springs of the pendula on the appearance of ILMs is examined. Increasing the values of the connecting spring constants may affect the excitation frequency range of ILMs and cause Hopf bifurcation to occur, followed by amplitude modulated motions (AMMs) including chaotic vibrations. The influence of the imperfections of the pendula on the system response is also investigated. Bifurcation sets are calculated to examine the influence of the system parameters on the excitation frequency range of ILMs and determine the threshold value for the connecting spring constant above which ILMs do not appear. Experiments were conducted for N = 2, and the data were compared with the theoretical results in order to confirm the validity of the theoretical analysis.

High Q factor over 3000 due to out-of-plane precession in nano-contact spin-torque oscillator based on magnetic tunnel junctions

We investigated microwave oscillation in a sombrero-shaped nano-contact spin-torque oscillator under an external magnetic field with an out-of-plane component. By increasing the out-of-plane field, we observed an abrupt change from in-plane precession to out-of-plane precession around the effective demagnetization field of the free layer. The out-of-plane precession under optimized conditions yielded not only a fundamental oscillation peak with a very large Q factor (3200) but also higher-order harmonic peaks with frequencies up to at least 45 GHz. A high Q factor and high-frequency oscillations are of great importance for device applications such as telecommunications, radar sensors, and high-speed magnetic field sensors.

Colpitts Oscillator: Design and Performance Optimization

From the very fundamental oscillator, a simple pendulum wherein there is a constant energy switch between potential and kinetic energy, oscillators have seen groundbreaking changes in setup, operation and their applicability. There are harmonic oscillators which produce a continuous sine wave output of certain frequencies as per the passive components involved. Additionally, are knownRelaxation oscillator which yield triangular, square and sawtooth waves as output to name a few.The present paper deals with the details of how a fundamental Colpitts oscillatory circuit can be designed. Furthermore, we would take a look at optimizing its performance with change in several dependent characteristics in oscillation. We would conclude with an inference pertaining to the best customization with could be put to practical usage.

Control of Vibrations in a Micromechanical Gyroscope Using Inertia Properties of Standing Elastic Waves

The characteristics of the dynamics and control of oscillations in a micromechanical ring resonator gyro that uses inertia properties of elastic waves are considered. A functional diagram of the gyroscope with a ring resonator is presented. Further, the scheme has a loop oscillation excitation and a measurement channel. This model is studied under the excitation of the resonator, which automatically provides maximum vibration amplitude with minimum control. It is shown that the using the schemes of stabilization of of the excited amplitude or normalisation secondary oscillations significantly reduces the non-linear characteristics of the transformation. To achieve the desired dynamic characteristics of the gyroscope, it is proposed to use feedback in the measuring channel by the velocity of radial displacement of the ring resonator in the output zone. The technique allows the calculation of the envelope of the fundamental mode oscillation from appropriate differential equations. That is a convenient tool for a comparative investigation of the gyro's characteristics while studying the direct measurement type and the compensation type.

Complex mode dynamics of coupled wave oscillators

We explore how nonlinear coherent waves localized in a few wells of a periodic potential can act analogously to a chain of coupled oscillators. We identify the small-amplitude oscillation modes of these "coupled wave oscillators" and find that they can be extended into the large amplitude regime, where some "ring" for long times. We also reveal the appearance of complex behavior such as the breakdown of Josephson-like oscillations, the destabilization of fundamental oscillation modes, and the emergence of chaotic oscillations for large amplitude excitations. We show that the dynamics may be accurately described by a discrete model with nearest-neighbor coupling, in which the lattice oscillators bear an effective mass.

240 GHz and 272 GHz Fundamental VCOs Using 32 nm CMOS Technology

Two fundamental oscillators, a 240 GHz and a 272 GHz are demonstrated using the IBM CMOS 32 nm process. The design of both oscillators was based on a Colpitts differential topology, where parasitic capacitances of the device are used as a part of the inductor-capacitor tank. The design process and consideration is discussed, as well as the measurement procedures. A simplified model predicting the output power of the voltage-controlled oscillator (VCO) and its phase noise is presented, and comparison to the measured results is discussed. An output power level of 0.2 mW ( <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex Notation="TeX">$-$</tex></formula> 7 dBm) was realized for the 240 GHz oscillator, with total power consumption of 13.3 mW and a total tuning range of 13.5 GHz achieved by changing both the gate and drain bias. The 272 GHz oscillator achieved a lower power level of about <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex Notation="TeX">$-$</tex></formula> 22 dBm, with a total power consumption of only 7 mW.

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.

A Class-F CMOS Oscillator

An oscillator topology demonstrating an improved phase noise performance is proposed in this paper. It exploits the time-variant phase noise model with insights into the phase noise conversion mechanisms. The proposed oscillator is based on enforcing a pseudo-square voltage waveform around the LC tank by increasing the third-harmonic of the fundamental oscillation voltage through an additional impedance peak. This auxiliary impedance peak is realized by a transformer with moderately coupled resonating windings. As a result, the effective impulse sensitivity function (ISF) decreases thus reducing the oscillator's effective noise factor such that a significant improvement in the oscillator phase noise and power efficiency are achieved. A comprehensive study of circuit-to-phase-noise conversion mechanisms of different oscillators' structures shows the proposed class-F exhibits the lowest phase noise at the same tank's quality factor and supply voltage. The prototype of the class-F oscillator is implemented in TSMC 65-nm standard CMOS. It exhibits average phase noise of -136 dBc/Hz at 3 MHz offset from the carrier over 5.9-7.6 GHz tuning range with figure-of-merit of 192 dBc/Hz. The oscillator occupies 0.12 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> while drawing 12 mA from 1.25 V supply.

Optical processing between two metallically hybrid microdisks

A waveguide is bridged between two metallically hybrid microdisks for achieving nonlocal optical processing. The whispering gallery mode (WGM) is split into two modes, one is intrinsic WGM and the other is oscillating mode (OM) whose photons oscillate between two microdisks through the waveguide. The characteristics of OM on the waveguide's width and length are studied. The results show the fundamental WGM oscillation only happens at certain lengths and widths of the waveguide, and strong optical interaction between two microdisks is accompanied by a high-loss waveguide. The optical processing through a waveguide between two individual resonators or photon producers may be applied to dynamic control on the photon states.

EVIDENCE OF MULTIPLE SLOW ACOUSTIC OSCILLATIONS IN THE STELLAR FLARING LOOPS OF PROXIMA CENTAURI

We present the first observational evidence of multiple slow acoustic oscillations in the post flaring loops of the corona of Proxima Centauri using XMM-Newton observations. We find the signature of periodic oscillations localized in the decay phase of the flare in its soft (0.3-10.0 keV) X-ray emissions. Using the standard wavelet tool, we find the multiple periodicities of 1261 s and 687 s. These bursty oscillations persist for durations of 90 minutes and 50 minutes, respectively, for more than 4 cycles. The intensity oscillations with the period of 1261 s may be the signature of the fundamental mode of slow magnetoacoustic waves with the phase-speed of 119 km s$^{-1}$ in the loop of the length 7.5$\times 10^{9}$ cm heated initially to obtain the flare peak temperature of 33 MK and later cooled down in the decay phase maintained at the average temperature of 7.2 MK. The other period of 687 s may be associated with the first overtone of slow magnetoacoustic oscillations in the flaring loop. The fundamental mode oscillations show a dissipation with damping time of 47 min. The period ratio P$_{1}$/P$_{2}$ is found to be 1.83 indicating that such oscillations are most likely excited in longitudinal density stratified stellar loops. We estimate the density scale height of stellar loop system as 22.6 Mm, which is smaller than the hydrostatic scale height of the hot loop system, and implies the existence of non-equilibrium conditions.

Potential Gravitational - Solar Electromagnetic Spectral Radiance Interaction as the Source of the Earth’s Background Free Oscillations

The origins of the continuous free oscillations of the whole earth have been attributed to coupling between the solid earth and atmosphere primarily through the fundamental spheroidal mode 0S29 oscillation of ~3.7 mHz. The origins of these interference patterns have been attributed to an excitation source just above the Earth’s surface. However, comparable surface oscillations have been measured in the Sun’s photosphere. The cube root of the product of the gravitational constant, the spectral radiance of the sun, and the square of the frequency produced an acceleration value that was identical to the measured amplitude of the free Earth oscillations (~0.4∙10-11 m∙s-2). The quantitative convergence suggests these narrow-band accelerations may emerge within the Sun-Earth system as it moves through galactic space.

Continuous-wave hybrid index-antiguided and thermal-guided planar waveguide laser

A continuous-wave index-antiguided planar waveguide laser with a 220 -μm Nd:YAG active layer is investigated. Robust fundamental mode oscillation in the antiguided direction is demonstrated with negligible thermal index focusing while in the orthogonal direction the laser is dominantly thermally guided. A maximum output power of 2.25 W is obtained with a slope efficiency of 43% and an optical efficiency of 39%. A model is developed for finding the fundamental mode of laser oscillation with arbitrary index antiguiding and gain guiding in orthogonal directions with simultaneous thermal index guiding. Experimental results are compared to theory with good agreement.

Potential Gravitational - Solar Electromagnetic Spectral Radiance Interaction as the Source of the Earth’s Background Free Oscillations

The origins of the continuous free oscillations of the whole earth have been attributed to coupling between the solid earth and atmosphere primarily through the fundamental spheroidal mode 0S29 oscillation of ~3.7 mHz. The origins of these interference patterns have been attributed to an excitation source just above the Earth’s surface. However, comparable surface oscillations have been measured in the Sun’s photosphere. The cube root of the product of the gravitational constant, the spectral radiance of the sun, and the square of the frequency produced an acceleration value that was identical to the measured amplitude of the free Earth oscillations (~0.4∙10-11 m∙s-2). The quantitative convergence suggests these narrow-band accelerations may emerge within the Sun-Earth system as it moves through galactic space.

A wind tunnel study of the effects of collision processes on the shape and oscillation for moderate-size raindrops

Drop–drop collision experiments were carried out at the Mainz vertical wind tunnel. Water drops of 2.5mm diameter were freely floated at their terminal velocities in a vertical air stream and collided with 0.5mm diameter droplets. The collisions were recorded with a high speed digital video camera at a frame rate of 1000 per second. Altogether 116 collision events were observed, 75 of which ended with coalescence, and the rest with filament type breakup. The coalescence efficiency and its dependence on the Weber number and on the eccentricity of the colliding drops showed good agreement with earlier numerical studies. Thirty-six recorded collisions were further analyzed in order to characterize the oscillation behavior of large drops after a collisional excitation. Besides the introduction of the experimental method for studying the raindrop collisions, the study primarily focused on the characterization of the average value and the amplitude of the axis ratio variation, the active oscillation modes and their frequencies, and the decay of the oscillations excited by the collision. In spite of the fact that the amplitude of the axis ratio variation increased up to 4 to 6 times of its value before collision – depending on whether the collision ended with coalescence or breakup –, the average axis ratios increased by less than 1%. Since the sizes of largest drops after collision remained practically unchanged during the collision process, the frequencies of the active fundamental (n=2) oscillation modes of the drops did not change significantly either. Instantaneously after collision the transverse oscillation mode and the whole body rotation dominated, while at a later instant the oblate–prolate mode determined again the drop shape alteration. It was further found that the damping of the oscillation after collision can be adequately described by the viscous decay of a liquid spherical drop.