Answers and Solutions

Answers and solutions to the puzzles in this issue

Strategic research initiative at the Research Techno Plaza

With novel synthesis methodologies, new molecules, and atomic scale engineering, tailored properties of materials yielding vastly superior electronic devices and even synthetic body parts seem to be within the realm of possibilities. The Advanced Materials Research Centre is a University-wide research centre that focuses on the synthesis of advanced and innovative functional materials for applications ranging from biotechnology to nanoelectronics. In addition optical, thermal and mechanical characterization of these materials to establish their functionality for the particular application needs to be evaluated. Towards this end, novel techniques for non-contact and wholefield characterization of materials have been developed

Development and integration of new ultra low k materials & processes for high reliability microelectronics

The project will focus on the integration of the ultra low k materials into advanced silicon processes so as to yield highly reliable devices to meet the requirements of next generation integrated circuits. Reliability initiatives will include phenomenon such as stress and electro migration, time dependent dielectric breakdown (TDDB), development of new methodologies to characterize the material properties such as adhesion strength, moisture absorption and hygrostress, and to study the impact of polymer materials as well as porosity on thermal conductivity, thermo mechanical stresses on the device as well as packaging levels. New designs and structures of ultra low k materials alternated with silicon dioxide and silicon nitride materials will be investigated in order to improve the reliability of the packaged flip chip interconnects. Finally, methodologies to study device and package level reliabilities with numerical modeling techniques will also be developed

High performance engineering materials

This project aims to characterize and compare the OTFT performance between the thermally grown oxide and sol-gel silica thin film as dielectric layer, as well as to yield OTFT devices exhibiting enhanced mobilities and excellent device characteristics at low operating voltage

Synthesis and characterization of new thieno[3,2-b]thiophene derivatives

Three derivatives of thieno[3,2-b]thiophene end-capped with phenyl units have been synthesized and characterized by MALDI TOF mass spectroscopy, elemental analysis, UV-vis absorption spectroscopy and thermogravimetric analysis (TGA). All compounds were prepared using Pd-catalyzed Stille or Suzuki coupling reactions. Optical measurements and thermal analysis revealed that these compounds are promising candidates for p-type organic semiconductor applications.Published versio

Synthesis of AgInS2 nanocrystal ink and its photoelectrical application

This paper reports a hot-injection method of preparing AgInS2 nanocrystals with different sizes and morphologies, starting with the capping agents of oleylamine and dodecylthiol, and varying the reaction conditions. The effects of the temperature and time on the growth of AgInS2 nanocrystals are investigated. These parameters have a tremendous impact on the size and morphology of the nanocrystals, allowing the controlled synthesis of shapes including nanoparticles and nanorods. It has been found that the size of the nanoparticles and nanorods can be controlled by changing the time of nanocrystal growth. The evolution from nanoparticles to nanorods can be controlled by the reaction temperature. The possible formation mechanism and growth process of the AgInS2 nanocrystals are discussed based on the experimental results. The AgInS2 nanocrystal ink with a bandgap of 1.90 eV can produce crack-free films. As a proof-of-concept, thin film solar cells made by using such AgInS2 films as absorber layers are tested for their viability as a type of solar cell material and are found to exhibit a measurable photovoltaic response

Dye-sensitized solar cells based on tin oxide nanowire networks

Highly crystalline tin oxide nanowires grown through vapor–liquid–solid process were used in Dye-Sensitized Solar Cells (DSSCs). Back-illuminated structure was adopted due to the opaqueness of silicon substrate used to grow the nanowires. To provides a good understanding of using metal oxide nanowires in DSSC structure, the physical properties of nanowires such as length and diameter on the effect of solar cells performance were investigated through comparison and normalization. It was found that increase the nanowire length will enhance the cell performance first by providing large surface area for dye attachment while still maintains the direct path for charge transport. However, nanowire with a length that is too long would have an adverse effect on the electron collection efficiency. Nanowires with larger diameter showed a significant increase of current density hence the cell performance resulted from less scattering centers along the relatively larger charge transport channel. Through optimization, nanowires grown from 10 nm thick Au catalyst with the thickness around 40 μm exhibited the best cell performance of 0.18%

Investigation of turn-on voltage shift in organic ferroelectric transistor with high polarity gate dielectric

Large positive shifts of turn-on voltage Vto were observed in ferroelectric organic thin film transistor using P(VDF-TrFE) copolymer (57–43 mol%) as gate insulator during OFF to ON state sweeping. The shift of the transfer characteristic up to +25 V is attributed to the accumulation of mobile charge carriers (holes) in pentacene layer even during the device OFF state. The observed phenomena were first discussed on the basis of a negative surface potential created by the dipole field of a polar dielectric and trap states in an organic semiconductor layer. It was however found that these were unable to fully address the observed strong Vto shift due to the presence of large polarization in the P(VDF-TrFE) layer. A mechanism of negative polarization-compensating charges which are injected to the insulator region next to the semiconductor layer was proposed and examined to understand the phenomenon. The turn-on voltage is found to change with different magnitude of positive voltage pulses, and corresponds to different amount of charges injected for compensation. Time measurement of drain current shows a transient decaying behavior when gate bias is switched from positive to negative polarity which confirms the trapping of negative charges in the insulator

Imparting photosensitivity through decoration of nanoparticle on reduced graphene oxide

Attachment of metal nanoparticles to reduced graphene oxide (rGO) results in formation of a hybrid material which opens a new pathway to positively modify rGO properties. We decorated rGO with gold nanoparticle (Au-rGO) and fabricated visible-light detector devices utilizing thin film of the hybrid material. We found that the photo current increases with illumination and decreases in dark. The photosensitivity of Au-rGO hybrid is explained by positive synergy of plasmonic gold nanoparticle with rGO as conduction matrix. This study explores the prospect of photo induced carrier transfer in rGO hybrid

Effect of plating parameters on the intrinsic stress in electroless nickel plating

With the increasing application of electroless nickel (EN) as a bumping or under-bumping metalization material, the microelectronic packaging engineers are required to have a deeper understanding and control of intrinsic stress in EN plating. The purpose of this work is to investigate the effect of some of the most important operating parameters on the formation of intrinsic stress during plating. The analysis of variances method was applied to obtain both single effects and compound effects of selected factors. Results indicate that high pH value and aged solution affect the intrinsic stress significantly, while surface roughness does not have much influence on the intrinsic stress for the range investigated. Aging at 190 °C for 170 h changes neither the Ni–P structure nor the intrinsic stress to a significant degree. Further investigation indicated that the intrinsic stress was probably related to the Ni–P microstructure as a result of the deposition rate. It was found that the higher the deposition rate, the higher the intrinsic stress.Accepted versio