Application of Internal Revenue Code Section 103(C) to Variable Rate Demand Bonds: Purging the Profiteering Potential

This Note analyzes transactions involving VRDBs, to determine whether they comply with the strictures of IRC section 103(c) and, hence, qualify for the tax exemption. Initially, this Note provides an overview of the tax-exempt bond market by examining the factors that led to the development of VRDBs. It then demonstrates how a reasonable interpretation of the language of IRC section 103(c), gleaned from its legislative history and Treasury promulgations, requires that almost all VRDBs lose their tax-exempt status. More specifically, this Note concludes that the inability to calculate the yield for VRDBs creates an impermissible potential to earn arbitrage profits. Based on this conclusion, this Note suggests that it is incumbent upon the Treasury Department to issue regulations that will limit the tax exemption for transactions involving VRDBs. Finally, this Note proposes measures that delineate the proper scope of the tax exemption for VRDBs and incorporates them in a model Treasury Regulation

Application of Internal Revenue Code Section 103(C) to Variable Rate Demand Bonds: Purging the Profiteering Potential

This Note analyzes transactions involving VRDBs, to determine whether they comply with the strictures of IRC section 103(c) and, hence, qualify for the tax exemption. Initially, this Note provides an overview of the tax-exempt bond market by examining the factors that led to the development of VRDBs. It then demonstrates how a reasonable interpretation of the language of IRC section 103(c), gleaned from its legislative history and Treasury promulgations, requires that almost all VRDBs lose their tax-exempt status. More specifically, this Note concludes that the inability to calculate the yield for VRDBs creates an impermissible potential to earn arbitrage profits. Based on this conclusion, this Note suggests that it is incumbent upon the Treasury Department to issue regulations that will limit the tax exemption for transactions involving VRDBs. Finally, this Note proposes measures that delineate the proper scope of the tax exemption for VRDBs and incorporates them in a model Treasury Regulation

A Raspberry Pi controlling neuromorphic hardware

This thesis describes the integration of a Raspberry Pi, a credit-card-sized single board computer, into the Wafer Scale Integration (WSI) System of the BrainScaleS project. The Raspberry Pi’s task is to bundle all the interfaces necessary to manage the system’s elaborate power supply into one single-access, easy-to-use interface. To this purpose the Raspberry Pi replaced the former evaluation board responsible for power management, taking over all of its tasks and in addition providing faster and cheaper hardware. The integration took place in two main steps: configuring the Raspberry Pi’s hardware and adapting the control programme from the former board to the new hardware. The results of this thesis are the successful integration of the Raspberry Pi into the WSI system, which was proven by several communication tests between the Raspberry Pi and the rest of the system, and an easy-to-follow step-by-step guide on how to set up Raspberry Pis to manage additional systems

Electrical Characterisation of III-V Nanowire MOSFETs

The ever increasing demand for faster and more energy-efficient electricalcomputation and communication presents severe challenges for the semiconductor industry and particularly for the metal-oxidesemiconductorfield-effect transistor (MOSFET), which is the workhorse of modern electronics. III-V materials exhibit higher carrier mobilities than the most commonly used MOSFET material Si so that the realisation of III-V MOSFETs can enable higher operation speeds and lower drive voltages than that which is possible in Si electronics. A lowering of the transistor drive voltage can be further facilitated by employing gate-all-around nanowire geometries or novel operation principles. However, III-V materials bring about their own challenges related to material quality and to the quality of the gate oxide on top of a III-V MOSFET channel.This thesis presents detailed electrical characterisations of two types of (vertical) III-V nanowire transistors: MOSFETs based on conventional thermionic emission; and Tunnel FETs, which utilise quantum-mechanical tunnelling instead to control the device current and reach inverse subthreshold slopes below the thermal limit of 60 mV/decade. Transistor characterisations span over fourteen orders of magnitude in frequency/time constants and temperatures from 11 K to 370 K.The first part of the thesis focusses on the characterisation of electrically active material defects (‘traps’) related to the gate stack. Low-frequency noise measurements yielded border trap densities of 10^18 to 10^20 cm^-3 eV^-1 and hysteresis measurements yielded effective trap densities – projected to theoxide/semiconductor interface – of 2x10^12 to 3x10^13 cm^-2 eV^-1. Random telegraph noise measurements revealed that individual oxide traps can locally shift the channel energy bands by a few millielectronvolts and that such defects can be located at energies from inside the semiconductor band gap all the way into the conduction band.Small-signal radio frequency (RF) measurements revealed that parts of the wide oxide trap distribution can still interact with carriers in the MOSFET channel at gigahertz frequencies. This causes frequency hystereses in the small-signal transconductance and capacitances and can decrease the RF gains by a few decibels. A comprehensive small-signal model was developed, which takes into account these dispersions, and the model was applied to guide improvements of the physical structure of vertical RF MOSFETs. This resulted in values for the cutoff frequency fT and the maximum oscillation frequency fmax of about 150 GHz in vertical III-V nanowire MOSFETs.Bias temperature instability measurements and the integration of (lateral) III-V nanowire MOSFETs in a back end of line process were carried out as complements to the main focus of this thesis. The results of this thesis provide a broad perspective of the properties of gate oxide traps and of the RF performance of III-V nanowire transistors and can act as guidelines for further improvement and finally the integration of III-V nanowire MOSFETs in circuits

Low-Frequency Noise in TFETs

Nanowire tunnel field-effect transistors (TFETs) were investigated by carrying out noise measurements and low-temperature DC measurements. The TFET tunnelling junction was realised by a GaSb/InAs heterojunction resulting in a broken band gap. TFET noise currents were measured at frequencies between 10 Hz and 1 kHz. The results imply that noise in TFETs at the current state of development is dominated by generation-recombination processes caused by traps in the gate oxide. Trap densities between 10^20 cm^-3 eV^-1 and 10^22 cm^-3 eV^-1 were extracted from the noise measurements. The temperature-dependent DC measurements show that the TFETs' off-current is sensitive to the temperature, with lower off-currents at lower temperatures. This indicates that it is not only the tunnelling junction which is governing the off-current. It is concluded that in the devices' off-state electrons can still tunnel into the channel area through the broken band gap but require additional thermionic excitation over the bent channel conduction band to constitute a current.The ever-growing demand for electronic devices in all areas of our lives can only be satisfied due to the constant development of today’s most essential of all active electronic devices – the metal-oxide-semiconductor field-effect transistor (MOSFET). However, its further development is drawing to an end, so coming up with alternatives is of utmost importance. One of the most promising ones is the tunnel field-effect transistor (TFET). A MOSFET basically is an electrical switch. The current between two of the device’s contacts – source and drain – can be controlled by a third contact, the gate. In digital applications, such as all our computers and smartphones, MOSFETs only switch between an on- and an off-state, meaning flowing current or almost no current, respectively. The ability to switch between these two states as fast as possible is what governs a MOSFET’s speed and energy-efficiency. Over the last 50 years MOSFETs have undergone constant development to increase these measures. Due to the underlying physical principles that MOSFETs are based on, this development is drawing to an end. In a MOSFET electrons have to overcome an energy barrier to establish a current. With the gate contact this barrier can be raised (off-state) or lowered (on-state). This principle establishing the current is at the same time the principle which limits further scaling of MOSFETs as there are always a few electrons which can overcome the barrier – even in the device’s off-state. The idea for TFETs to overcome this limit is to control the current by opening or closing a narrow gap in the energy structure of the device. Instead of overcoming a barrier the electrons have to tunnel through it. In contrast to the MOSFET structure the electrons on the source side of the TFET structure face a restriction from the top which reduces the off-current. In my thesis I contribute to the development of TFETs as successors of or complements to MOSFETs by examining electrical noise and the current temperature dependence in TFETs. A well-known form of electrical noise is noise which finds its way into an audio signal (e. g. buzzing speakers). However, noise is present in all electrical signals and examining the noise in TFETs gives information about which parts of the devices require particular improvement to finally lead to industrially applicable TFETs benefitting the broad public

The Comparative Biochemistry of Mammalian and Insect Acetylcholinesterase with Reference to the Selective Inhibition by Organophosphates and Carbamates

Acetylcholinesterases from bovine erythrocytes and housefly heads are compared with respect to binding of substrates and reversible cationic inhibitors, effects of the latter on reaction with methane sulfonyl fluoride, and inactivation by organophosphofus and carbamate inhibitors. The observations show that a hydrophobic region is present outside the catalytic centre, which is considerably broader and more accessible in the insect enzyme. Phosphate and carbamate inhibitors can interact productively with this region, whereas such interactions would be detrimental to true substrates, diminishing their rates of reaction. It is this broader hydrophobic region, rather than wider separation of the anionic and esteratic sites, that accounts for acceleration of methane sulfonyl fluoride reaction by large cations and accommodation of bulky irreversible inhibitors in fly acetylcholinesterase. It is concluded that the greater selectivity for fly acetylcholinesterase of many organophosphates and carbamates may primarily depend on recognition of distinctive features around, rather than in, the active centre

The Comparative Biochemistry of Mammalian and Insect Acetylcholinesterase with Reference to the Selective Inhibition by Organophosphates and Carbamates

Acetylcholinesterases from bovine erythrocytes and housefly heads are compared with respect to binding of substrates and reversible cationic inhibitors, effects of the latter on reaction with methane sulfonyl fluoride, and inactivation by organophosphofus and carbamate inhibitors. The observations show that a hydrophobic region is present outside the catalytic centre, which is considerably broader and more accessible in the insect enzyme. Phosphate and carbamate inhibitors can interact productively with this region, whereas such interactions would be detrimental to true substrates, diminishing their rates of reaction. It is this broader hydrophobic region, rather than wider separation of the anionic and esteratic sites, that accounts for acceleration of methane sulfonyl fluoride reaction by large cations and accommodation of bulky irreversible inhibitors in fly acetylcholinesterase. It is concluded that the greater selectivity for fly acetylcholinesterase of many organophosphates and carbamates may primarily depend on recognition of distinctive features around, rather than in, the active centre