Pin Jern Ker

High speed low noise InAs electron avalanche photodiodes for telecommunication and infrared sensing applications

The leakage current, avalanche gain, excess noise and frequency response of InAs avalanche photodiodes (APDs) were investigated. Despite having a narrow bandgap, InAs APDs, which were fabricated using optimized fabrication procedures and surface passivation technique, were able to provide reasonably low leakage current for practical applications. The exponentially rising avalanche gain with increasing bias voltage without a classical avalanche breakdown exhibited its electron-dominated impact ionization characteristic and avalanche gain as high as 165 was measured. The excess noise or avalanche noise was found to be independent of gain and temperature with the excess noise factors fluctuating between 1.45 and 1.6 at high gain. The 3-dB bandwidth of InAs APDs was determined to be ~ 3.5 - 4 GHz and it was highly possible that the surface passivation dielectric and the unavailability of a lattice-matched semi-insulating substrate were the major limiting factors. However, unlike other mature APDs technologies, the 3-dB bandwidth of InAs APDs remained constant even up to the highest achievable avalanche gain, providing a record high gain-bandwidth product of ~ 580 GHz.

Modeling and simulation of InAs photodiode on electric field profile and dark current characteristics

This work reports the dark current density-voltage (J-V) characteristics and electric field profile of InAs photodiode with 100μm × 1μm cross sectional area at a temperature of 300K. The device structure was simulated using 2D SILVACO software and the model was used to determine all the optimum material physical parameters based on the parameters reported in other literatures. Dark current mechanisms, which include drift-diffusion current, generation-recombination current, trap-assisted tunneling current and band-to-band tunneling current, were incorporated into the ATLAS electrical characteristics model. Simulated dark current results were compared with the experimental results that were obtained from InAs photodiodes fabricated from molecular beam epitaxy (MBE) and metal organic vapor phase epitaxy (MOVPE) grown InAs wafers. Good agreement is found between the simulation and experimental results.

Modeling of 14 nm gate length n-Type MOSFET

Metal-Oxide-Semiconductor Field Effect Transistors MOSFETs (MOSFETs) transistor have been scaled tremendously through Moores Law since 1974 in order to compact transistors in a single chip. Thus, a proper scaling technique is compulsory to minimize the short channel effect (SCE) problems. In this paper, the virtual fabricated design and devices characterization of 14 nm HfO2/WSi2 n-type MOSFET device is presented. The device is scaled based on previous research on 32 nm transistors. The virtual fabrication and simulation of n-type MOSFETs are implemented using Virtual Wafer Fabrication (VWF) Silvaco TCAD Tools named ATHENA and ATLAS. From the simulation, result shows that the optimal value of threshold voltage (VTH), drive current (ION) and leakage current (IOFF) are 0.232291 V, 78.922×10-6 A/um and 77.11×10-9 A/um respectively. These simulation results are believed to be able to create a touchstone towards the optimization and fabrication of 14 nm devices gate length utilizing High-K/Metal Gate n-type MOSFET in impending work.

GPS-based highway toll collection system: Novel design and operation

Abstract The requirement for vehicles to halt for toll fee payment results in traffic congestion and reduces fuel efficiency. In this paper, hardware and software designs were involved to develop a GPS-based highway toll collection system. The system utilised the Raspberry Pi 2 as the microcontroller. Additional electronic modules such as GPS module, LCD module, speaker, wireless Wi-Fi router modem and wireless Wi-Fi adapter were included to perform specific tasks. The system utilised GPS coordinates to track vehicle and toll fees were incurred at predefined points. The travel summary was recorded in the online database. Furthermore, an automatic delay time adjustment system was studied and was implemented to reduce the power consumption of the system without compromising the accuracy. A personal cloud server was configured to allow online access of travel logs. The developed system promises motorists a smooth travel journey and eliminates the construction of expensive toll booths.

Smart home design with XBee Wi-Fi and Android-based graphical user interface

The smart home concept has constantly gained popularity over the past decades following the advent of technology. However, concerns on flexibility and infrastructure requirements discourage the widespread implementation of this concept. This project aims to improve the overall experience of a smart home by integrating the Wi-Fi IEEE 802.11 wireless communication standard into a standard smart home sensory network. The tasks of the project were centred on the development of a Wi-Fi integrated smart home system with a PIC® microcontroller and a Wi-Fi module as the core components. Additional components such as light-dependent resistor (LDR), temperature sensor, light-emitting diodes (LEDs) and DC motor were included to mimic a real life home environment. A custom designed Android graphical user interface (GUI) application was also developed to enable automated and manual control of the modelled smart home. The final smart home prototype presented the integration of Wi-Fi into a smart home network that grants users with greater flexibility while preserving the existing smart home experience.

Determining the inhibitor content of transformer insulating oil using UV-Vis spectroscopy

Monitoring and inspection of inhibitor content in transformer insulating oil has been a routine test for power utilities. Although new uninhibited transformer insulating oil contains naturally occurring inhibitors, these inhibitors could deplete over time during operation. Once the inhibitor depleted completely, the oil would start to deteriorate at a faster rate and eventually could lead to faults in transformer. The common method of determining the weight percentage of inhibitor in transformer oil is through Fourier Transform Infrared (FTIR) spectroscopy. However, this method is laboratory-based, which means oil sampling at site is necessary and the oil samples need to be transported to the laboratory. The necessity for oil sampling, coupled with the high cost of FTIR equipment have led to high maintenance cost. Therefore, this work investigated the possibility of using single wavelength or waveband optical detection for the determination of weight percentage of inhibitor in transformer oil using ultraviolet-visible-near infrared (UV-VIS-NIR) spectroscopy. Result of the work shows that the samples with inhibitor produced an absorbance peak at 1403nm. The peak absorbance of the spectral response is proportional to the weight percentage of inhibitor content that was measured using the conventional method, which is IEC 60666. An equation was derived to model the peak absorbance and weight percent of inhibitor content (%IC) of the oil and it was verified with additional oil sample with a known weight percent of Inhibitor content.

Determining the color index of transformer insulating oil using UV-Vis spectroscopy

The changes in color of the transformer oil have been used as measuring tools in determining the condition, performance and health of the transformer. Currently, the determination of color index is done by using a color comparator based on American Society for Testing and Materials (ASTM) D 1500 standard. This technique requires the tester or observer to compare the samples with two ASTM color references. Color is subjective and each individual could report a different color index. It could cause an error of 0.5 color index since the index difference between two consecutive ASTM color references is 0.5. Therefore, this work proposes the determination of color index of insulating oil using ultraviolet to visible (UV-Vis) Spectroscopy to eliminate any human handling error and improve the accuracy of the color index readings. Absorbance spectral responses of oils with different color index were used to correlate the color index with the absorbance spectral response of oil. Results show that the bandwidth of the absorbance spectral response is proportional to the color index of the oil. Modeled equation was developed to relate the bandwidth and color index of the oil. The equation was tested and verified by measuring the optical absorbance of another batch of transformer oil samples and inputting the bandwidths to obtain the color indices.

Development of a GPS-based highway toll collection system

The necessity for vehicles to stop or slow down for toll fee payment results in traffic congestion and reduces fuel efficiency. Hence, a system that enables road users to pay the toll fees without stopping or slowing down was proposed and developed. Hardware and software designs were carried out to develop a Global Positioning System (GPS)-based highway toll collection system. This system was developed using a Raspberry Pi 2 microcontroller. Different modules such as GPS module, Liquid Crystal Display (LCD) module, speaker, wireless Wi-Fi router modem and wireless Wi-Fi adapter were incorporated and integrated with the microcontroller to perform a few specific functions. In general, the system utilized GPS coordinates to detect whether a vehicle passed through predefined locations in the database and the travel details were recorded. The Raspberry Pi 2 microcontroller was configured as a personal cloud server to allow online access of travel logs. This developed system presents a different approach for highway toll collection which eliminates travel delays and construction of expensive gantries or toll booths.

A microcontroller-based system for liquid level detection using infrared sensing

This project aims at developing an intelligent liquid level detection system using the concept of infrared optical sensing. It involves a comprehensive study on the optical transmittance of water and Polyethylene Terephthalate (PET), and the integration of optical monitoring hardware system with software development to implement the concept of infrared optical sensing for liquid level detection. An extensive study was done and it was determined that for this system, the optical transmittance of water should be low while the optical transmittance of PET should be high. The optical spectrum which is suitable for this application was determined to be in the range of 1350nm to 1500nm. A signal conditioning circuitry was designed to channel the signal from the photodetector to the microcontroller. A program was developed using C-programming language in order to carry out all the input/output control functions. A graphical user interface (GUI) was designed to interface with the microcontroller such that the system was user-friendly. Furthermore, a driver circuitry was designed to provide stable voltage and current supply to the laser diode that was acting as the infrared light source.