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 (Phi(metal)) using self-assembled monolayer (SAM) of metallated porphyrins. Porphyrin SAM was prepared on SiO(2) 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 degrees C. Temperature stability experiments on MOSCAPs show that the above method can be effectively implemented in advanced CMOS technologies involving the gate-last process

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

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 interlayer 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 ILD's 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

Modification of Electronic Properties of Graphene with Porphyrin Self-Assembled Monolayers and Photoinduced Interactions

Solution processable reduced graphene oxide (RGO), with its unique electrical and structural properties is being considered in large scale device fabrication. The research developments in the formation and characterization of nanoelectronic devices with self-assembled monolayers (SAMs) of porphyrin can have foundations for future high speed electronics, alternative energy sources and sensors. In this work, we present the effect porphyrin monolayer functionalization on the electronic properties of RGO. Electrical transport measurements show that this dipolar monolayer on RGO induces doping and the capacity to tune the electronic properties of RGO may have important applications in future graphene devices, sensors and energy harvesting. Also, carrier transfer from excited zinc porphyrin molecules to carbon-based nanostructures is demonstrated on transistors comprising physiosorbed RGO on zinc porphyrin SAM

Effect of Central Metal Ion on Molecular Dipole in Porphyrin Self-Assembled Monolayers

The physical and electronic properties of nano-scale semiconductor devices are mainly decided by their surfaces and interfaces. Use of dipolar self-assembled monolayer (SAM) on semiconductor/oxide interfaces has an enormous potential to tailor the behavior of nanoelectronic, optical and biological devices. Among different molecules, porphyrins have been identified to form chemically stable SAMs on different substrates and their dipolar properties can be tuned by incorporating various metal species in them. This allows work-function tuning according to various technological needs. In this paper, we describe the effect of central metal ion (selected period-4 transition metal ions Zn, Cu, Ni, Fe and Co) incorporated in 5-(4-hydroxyphenyl)-10,15,20-tri(p-tolyl)porphyrin (TTPOH) on the surface potential using Kelvin probe microscopy. Density functional theory (DFT) calculations were performed to estimate the magnitude of dipole moments. Also, absorption spectra of TTPOH molecule and its metal derivatives are compared

Facile fabrication of graphene devices through metalloporphyrin induced photocatalytic reduction

Solution processed graphene oxide (GO) sheets are electronically insulating and are generally reduced by chemical treatment or heat treatment in a reducing environment to recover their electronic properties, forming reduced graphene oxide (rGO). Here, GO sheets were photocatalytically reduced using 5-(4-hydroxyphenyl)-10,15,20-tri(p-tolyl) zinc(II) porphyrin (Zn(II)TTPOH) under ambient conditions. After illumination in the presence of a hole scavenger and Zn(II)TTPOH, the formation of rGO was confirmed through optical absorption measurements and monitoring of the D/G peak ratios from Raman measurements. The resultant rGO formed stable aqueous suspensions with the Zn(II)TTPOH. The electron transfer from photoexcited porphyrin to GO was studied through photoluminescence measurements. Utilising this photoreduction process as a post processing strategy, an increase in conductivity and an ambipolar field effect transistor (FET) behaviour were demonstrated on prepatterned GO devices. We have also confirmed the photoreduction process at low energy wavelengths (588 nm), indicating the versatility of using metalloporphyrins as photocatalysts for graphene oxide reduction

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 Young's 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

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

Organic field effect transistors based on poly(3-hexylthiophene) and Cu(II) 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 (I(on)) 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,23H-porphyrin 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 N-2, CO2, O-2, ethanolamine, N2O, and moisture. The sensor has exhibited a fast response and recovery times and is fully recoverable after repeated exposures