Mrunal A. Khaderbad

Effect of annealing on the magnetic properties of Gd focused ion beam implanted GaN

The authors have studied the effect of annealing on the magnetic and the structural properties of Gd focused ion beam implanted GaN samples. Molecular beam epitaxy grown GaN layers, which were implanted with 300keV Gd3+ ions at room temperature at doses 2.4×1011 and 1.0×1015cm−2, are rapid thermally annealed in flowing N2 gas up to 900°C for 30s. X-ray diffraction results indicate the presence of Ga and N interstitials in the implanted layers. Their densities are also found to reduce upon annealing. At the same time, magnetic measurements on these samples clearly show a reduction in the saturation magnetization as a result of the annealing for the lowest Gd incorporated sample, while in the highest Gd incorporated sample it does not change. These findings suggest that Gd might be inducing magnetic moment in Ga and/or N interstitials in giving rise to an effective colossal magnetic moment of Gd and the associated ferromagnetism observed in Gd:GaN.

Explosive vapor sensor using poly (3-hexylthiophene) and CuII tetraphenylporphyrin composite based organic field effect transistors

Organic field effect transistors based on poly(3-hexylthiophene) and CuII tetraphenylporphyrin composite were investigated as sensors for detection of vapors of nitrobased explosive compounds, viz., 1,3,5-trinitro-1,3,5-triazacyclohexane (RDX), 2,4,6-trinitrotoluene (TNT), and dinitrobenzene, which are also strong oxidizing agents. Significant changes, suitable for sensor response, were observed in transistor “on” current (Ion) and conductance (S) after exposure. A similar device response was, however, not observed for oxidizing agents such as benzoquinone and benzophenone. The Fourier transform infrared spectrometry experiments supported the results, where exposure to RDX and TNT vapors resulted in a significant shift in IR peaks.

Piezoresistive SU-8 Cantilever With Fe(III)Porphyrin Coating for CO Sensing

Carbon monoxide detection is required for various healthcare, environmental, and engineering applications. In this paper, 5,10,15,20-tetra (4,5-dimethoxyphenyl)-21H,23-Hporphyrin iron(III) chloride (Fe(III)porphyrin) coated on a piezoresistive SU-8 microcantilever has been used as a CO sensor. Rapid detection of CO down to 2 ppm has been observed with aforementioned sensors. Cantilevers without Fe(III)porphyrin have not responded to CO exposure. Fe(III)porphyrin-coated cantilever selectivity toward CO has been analyzed by measuring the sensor response to various gases such as N2, CO2, O2, ethanolamine, N2O, and moisture. The sensor has exhibited a fast response and recovery times and is fully recoverable after repeated exposures.

Electrical actuation and readout in a nanoelectromechanical resonator based on a laterally suspended zinc oxide nanowire.

In this paper, we present experimental results describing enhanced readout of the vibratory response of a doubly clamped zinc oxide (ZnO) nanowire employing a purely electrical actuation and detection scheme. The measured response suggests that the piezoelectric and semiconducting properties of ZnO effectively enhance the motional current for electromechanical transduction. For a doubly clamped ZnO nanowire resonator with radius ~10 nm and length ~1.91 µm, a resonant frequency around 21.4 MHz is observed with a quality factor (Q) of ~358 in vacuum. A comparison with the Q obtained in air (~242) shows that these nano-scale devices may be operated in fluid as viscous damping is less significant at these length scales. Additionally, the suspended nanowire bridges show field effect transistor (FET) characteristics when the underlying silicon substrate is used as a gate electrode or using a lithographically patterned in-plane gate electrode. Moreover, the Youngs modulus of ZnO nanowires is extracted from a static bending test performed on a nanowire cantilever using an AFM and the value is compared to that obtained from resonant frequency measurements of electrically addressed clamped–clamped beam nanowire resonators.

Porphyrin Self-Assembled Monolayer as a Copper Diffusion Barrier for Advanced CMOS Technologies

This paper investigates properties of zinc porphyrin self-assembled monolayer (SAM) as a Cu diffusion barrier for advanced back-end complementary metal-oxide-semiconductor technologies. The SAM layers are integrated with various inter-layer dielectrics (ILDs) such as HSQ and black diamond (BD). Monolayer formation on ILDs was studied using X-ray photoelectron spectroscopy, atomic force microscopy, contact angle, FTIR, and UV-Vis techniques. Degradation study of the Cu/ILD and Cu/SAM/ILD systems was performed using stress-induced CV and IV at elevated temperatures. Time-of-flight secondary ion mass spectrometry was employed to establish effectiveness of these films as Cu diffusion barriers. The results indicate that SAM films, in addition to improving the ILDs moisture resistance, may help in thinning down the existing barrier layer thickness on the low-k porous ILDs. Effect of SAM layers on the mechanical properties of BD film was studied using nanoindentation.

Variable Interface Dipoles of Metallated Porphyrin Self-Assembled Monolayers for Metal-Gate Work Function Tuning in Advanced CMOS Technologies

This paper presents a technique for continuous tuning of the metal-gate work function (¿metal) using self-assembled monolayer (SAM) of metallated porphyrins. Porphyrin SAM was prepared on SiO2 followed by Al evaporation to form MOS capacitors (MOSCAPs). The variation in the dipole moment achieved by changing the central metal ion (Zn, Cu, Ni, and Co) in metallated porphyrins has been shown as a way to modify the gate work function. Thermal gravimetric analysis (TGA) on Zn-porphyrin shows that the molecule is stable upto 450°C. Temperature stability experiments on MOSCAPs show that the above method can be effectively implemented in advanced CMOS technologies involving the gate-last process.

Fabrication of unipolar graphene field-effect transistors by modifying source and drain electrode interfaces with zinc porphyrin.

We report a unipolar operation in reduced graphene oxide (RGO) field-effect transistors (FETs) via modification of the source/drain (S/D) electrode interfaces with self-assembled monolayers (SAMs) of 5-(4-hydroxyphenyl)-10,15,20-tri-(p-tolyl) zinc(II) porphyrin (Zn(II)TTPOH) molecules. The dipolar Zn(II)TTPOH molecules at the RGO/platinum (Pt) S/D interface results in an increase of the electron injection barrier and a reduction of the hole-injection barrier. Using dipole measurements from Kelvin probe force microscopy and highest occupied molecular orbital-lowest unoccupied molecular orbital (HOMO-LUMO) calculations from cyclic voltammetry, the electron and hole injection barriers were calculated to be 2.2 and 0.11 eV, respectively, indicating a higher barrier for electrons, compared to that of holes. A reduced gate modulation in the electron accumulation regime in RGO devices with SAM shows that unipolar RGO FETs can be attained using a low-cost, solution-processable fabrication technique.

Metallated Porphyrin Self Assembled Monolayers as Cu Diffusion Barriers for the Nano-Scale CMOS Technologies

In this paper we have studied the application of metallated porphyrin self assembled monolayers (SAMs) as Cu diffusion barriers for ultra-large scale integration (ULSI) CMOS applications. The results for Cu/SiO2/Si and Cu/SAM/SiO2/Si MOS CAP structures are compared through a detailed electrical characterization of threshold voltage shift using bias-temperature studies. Material characterization and surface morphology is studied using UV absorption spectra and AFM. Our results show that metallated porphyrin SAMs can be effectively used as Cu diffusion barriers for ULSI applications.

Hydroxy-phenyl Zn(II) porphyrin self-assembled monolayer as a diffusion barrier for copper-low k interconnect technology

In this paper, we have studied the application of metallated porphyrin self-assembled monolayer (SAM) as a copper diffusion barrier for low-k inter-metal dielectric (IMD) CMOS technologies. SAM formed on hydrogen silesquioxane (HSQ), which is a low-k dielectric, has been demonstrated to be effective in preventing diffusion of copper ions into the porous dielectric. This has been shown by fabricating Cu-HSQ-Si and Cu-SAM-HSQ-Si metal-insulator-semiconductor test structures. Bias-temperature stress (BTS) studies have been done to investigate the effectiveness of SAM as a diffusion barrier. Formation of SAM on HSQ has been characterized using Fourier Transform Infra-red Spectroscopy studies. Thermogravimetric analysis (TGA) of hydroxyl-phenyl Zn(II) porphyrin has been used to verify thermal stability of the molecule under back-end-of-line (BEOL) process conditions.

Bottom-up method for work function tuning in high-k/metal gate stacks in advanced CMOS technologies

In this paper we have studied the application of porphyrin self-assembled monolayers (SAMs) for metal-gate work function tuning in high-k/metal gate technologies. Varying the dipole moment in porphyrin macrocycles by changing its central metal ion has been used to modify the work function. For HFCV analysis, porphyrin SAM was prepared on MOCVD grown hafnium oxide (HfO2) and on sputtered aluminum oxide (Al2O3) gate oxides followed by Al evaporation to form MOS capacitors. UV absorption and FTIR spectra show the formation of SAM on high-k while the thermal gravimetric analysis (TGA) on Zn-porphyrin shows that the molecule is stable upto 450°C and can be effectively implemented in high-k/metal gate technologies involving gate-last CMOS processes.