Daniel J. Arenas

A 410GHz CMOS Push-Push Oscillator with an On-Chip Patch Antenna

The uses of terahertz systems (300 GHz to 3 THz) in radars, remote sensing, advanced imaging, and bio-agent and chemical detection have been extensively studied. A compact and low-cost signal source is a key circuit block of terahertz systems. Traditionally, the circuits have been built using highly optimized III-V technologies. With the advances of CMOS, it has become realistic to consider terahertz circuits in CMOS. This paper reports a signal source operating near 410 GHz that is fabricated using low-leakage transistors in a 6 M 45 nm digital CMOS technology.

Low-Band-Gap Platinum Acetylide Polymers as Active Materials for Organic Solar Cells

We report on two pairs of platinum acetylide based polymers and model oligomers utilizing a 2,1,3-benzothiadiazole (BTD) acceptor moiety flanked on either side by either 2,5-thienyl donor units (Pt2BTD-Th and p-PtBTD-Th) or (3,4-ethylenedioxy)-2,5-thienyl donors (Pt2BTD-EDOT and p-PtBTD-EDOT). Both oligomer/polymer pairs absorb strongly throughout the visible region; however, because the (ethylenedioxy)thiophene moiety is a stronger donor than thiophene, the latter oligomer/polymer pair has a correspondingly lower band gap and, therefore, harvests light more efficiently at longer wavelengths. p-PtBTD-Th exhibits a relatively narrow molecular weight distribution with a number-average molecular weight (Mn) of 22 kDa, while p-PtBTD-EDOT exhibits a comparable Mn of 33 kDa but has a high polydispersity index likely due to aggregation. We provide a complete report of the photophysical and electrochemical characterization of the two oligomer/polymer pairs. The photophysical studies reveal that the materials undergo relatively efficient intersystem crossing. In a discussion of the energetics of photoinduced electron transfer from the platinum polymers to [6,6]-phenyl C61 butyric acid methyl ester (PCBM), it is noted that while the singlet state is quenched efficiently, the triplet state is not quenched, indicating that charge generation in the photovoltaic materials must ensue from the singlet manifold. Finally, organic photovoltaic devices based on blends of p-PtBDT-Th or p-PtBDT-EDOT with PCBM were characterized under monochromatic and simulated solar (AM1.5) illumination. Optimized devices exhibit an open-circuit voltage (Voc) of approximately 0.5 V, a short-circuit current density (Isc) of approximately 7.2 mA cm(-2), and a fill factor of approximately 35%, which yields overall power conversion efficiencies of 1.1-1.4%.

Towards terahertz operation of CMOS

The electromagnetic spectrum between 300GHz and 3THz is broadly referred as terahertz [1]. The utility of this portion of spectrum for detection of chemicals and bio agents, for imaging of concealed weapons, cancer cells and manufacturing defects [1, 2], and for studying chemical species using electron paramagnetic resonance, as well as, in short range radars and secured high data rate communications has been demonstrated. However, high cost and low level of integration for III–V devices needed for the systems have limited their wide use. The improvements in the high frequency capability of CMOS have made it possible to consider CMOS as a lower cost alternative for realizing the systems that can greatly expand the use of this spectrum range.

Infrared Optical Properties of Amorphous and Nanocrystalline Ta2O5 Thin Films

The optical constants of tantalum pentoxide (Ta2O5) are determined in a broad spectral region from the visible to the far infrared. Ta2O5 films of various thicknesses from approximately 170 to 1600 nm are deposited using reactive magnetron sputtering on Si substrates. X-ray diffraction shows that the as-deposited films are amorphous, and annealing in air at 800 °C results in the formation of nanocrystalline Ta2O5. Ellipsometry is used to obtain the dispersion in the visible and near-infrared. Two Fourier-transform infrared spectrometers are used to measure the transmittance and reflectance at wavelengths from 1 to 1000 μm. The surface topography and microstructure of the samples are examined using atomic force microscopy, confocal microscopy, and scanning electron microscopy. Classical Lorentz oscillators are employed to model the absorption bands due to phonons and impurities. A simple model is introduced to account for light scattering in the annealed films, which contain micro-cracks. For the unanneale...

Magnetite: Raman study of the high-pressure and low-temperature effects

We report the results of a low-temperature (300 K-15 K) high-pressure (up to 22 GPa) Raman study of the Verwey transition in magnetite (Fe3O4). We use additional Raman modes observed below the Verwey transition to determine how the transition temperature changes with the quasihydrostatic pressure. Increase of the pressure results in the linear decrease of the Verwey transition temperature, with no discontinuity. The corresponding pressure coefficient dT(v)/dP is found to be -5.16 +/- 1.19 K/GPa. Such a decrease is substantially larger than the one predicted by the mean-field Coulomb interaction model of the transition. (c) 2005 American Institute of Physics.

Magnetodielectric coupling of infrared phonons in single-crystal Cu2OSeO3

Reflection and transmission as a function of temperature (5-300 K) have been measured on a single crystal of the magnetoelectric ferrimagnetic compound Cu2OSeO3 utilizing light spanning the far infrared to the visible portions of the electromagnetic spectrum. The complex dielectric function and optical properties were obtained via Kramers-Kronig analysis and by fits to a Drude-Lortentz model. The fits of the infrared phonons show a magnetodielectric effect near the transition temperature (T-c similar to 60 K). Assignments to strong far-infrared phonon modes have been made, especially those exhibiting anomalous behavior around the transition temperature.

Magnetic and transport measurements on the layered III-VI diluted magnetic semiconductor In1−xMnxSe

Magnetic and transport properties of single-crystalline In1−xMnxSe (x=0.01 and 0.10) have been measured. In1−xMnxSe exhibits a prominent magnetization hysteresis between 90 and 290K. In1−xMnxSe is conducting with increasing resistance at low temperatures and a small hysteresis between 90 and 290K with the cooling trace having lower resistivity. The magnetization above and below the hysteresis is consistent with a paramagnetic signal. A Curie–Weiss fit to the data yields a value of Jeff∕kB=−240K. The data are consistent with a saturated component contributing to the hysteresis and a paramagnetic phase that scales with concentration.

Magnetic measurements on ferromagnetic behavior in the bulk II-VI diluted magnetic semiconductor Zn1-xCrxTe

Magnetic measurements on the ferromagnetic behavior in the bulk II–VI diluted magnetic semiconductor Zn1−xCrxTe were made on two x=0.0033 single crystals taken from different regions of the same boule. Ferromagnetism was verified in both samples by an Arrott plot analysis with a transition temperature at 365 K (well above room temperature). For both samples at room temperature, the coercive field is ∼0.0100 T and the remanent magnetization is 23% of the saturated value. The similarity in the observed ferromagnetic behavior between the two samples suggests that a stable CryTez or possibly ZnxCryTez precipitate phase is responsible, although a Cr-rich region in the bulk Zn1−xCrxTe itself cannot currently be conclusively ruled out as the source.

Broadband Dielectric Characterization of Aluminum Oxide (Al2O3)

Applications for low-temperature cofired ceramics (LTCC) and high-temperature cofired ceramics (HTCC) are advancing to higher frequencies. In order to design ceramic microsystems and electronic packages, the electrical properties of materials must be well characterized over a broad frequency range. In this study, the dielectric properties of commercial aluminum oxide (Al2O3) with different glass loadings are characterized using three different measurement techniques: the split-post cavity, terahertz (THz) time-domain spectroscopy, and Fourier transform IR spectroscopy (FTIR). Specifically, the dielectric properties will be characterized from 10 GHz to IR frequencies. A split-post cavity was employed for determination of dielectric properties in the 10 GHz range. A broadband THz spectroscopy technique was used to characterize the specimens using measured time-domain transmission data. The dielectric constant and loss were extracted from the samples frequency-domain transmission characteristics, providing ...

Components for generating and phase locking 390-GHz signal in 45-nm CMOS

Components for generating and phase locking 390-GHz signal are demonstrated using low leakage transistors in 45-nm CMOS. An integrated chain of circuits composed of an 195-GHz oscillator with frequency doubled output at ~390 GHz followed by two cascaded ÷2 injection locked frequency dividers with output frequency of ~49 GHz is demonstrated. The peak power radiated at ~390 GHz by an on-chip antenna is ~2 μW. The oscillator and frequency divider consumes 21 and 6 mW, respectively.