Comparative analysis of VDMOS/LDMOS power transistors for RF amplifiers

A comparison between the RF performance of vertical and lateral power MOSFETs is presented. The role of each parasitic parameter in the assessment of the power gain, 1-dB compression point, efficiency, stability, and output matching is evaluated quantitatively using new analytical expressions derived from a ten-element model. This study reveals that the contribution of the parasitic parameter on degradation of performance depends upon the specific technology and generic perceptions of source inductance and feedback capacitance in VDMOS degradation may not always hold. This conclusion is supported by a detailed analysis of three devices of the same power rating from three different commercial vendors. A methodology for optimizing a device technology, specifically for RF performance and power amplifier performance is demonstrated

Strategies and economics of farming systems with coffee in the Atlantic Rainforest Biome

In the Zona da Mata of Minas Gerais State, Brazil, family farmers are adjusting to agroecological principles to reconcile sustainable agriculture, livelihood improvements and biodiversity conservation. Starting in 1993, experimentation with coffee agroforestry was gradually initiated on an increasing number of farms (37 in total), resulting in the simultaneous management of sun coffee (SC) and agroforestry coffee (AF) plots. We aimed (1) to identify factors that determine the farmers’ selection of trees used in AF; (2) to describe the agroecological farms in transition; and (3) to perform an economic comparison between AF and SC. These objectives were addressed by combining data from botanical surveys in 1993/1994 and 2007, by interviews with farmers and by detailed data on the production value and costs of labour and material inputs. The results showed considerable diversity in farming strategies and management among the farmers. Early adopters of AF had diversified towards production of different marketable products. The use of native trees in AF for this purpose, and for restoration of soil fertility (e.g., leguminous trees), had increased since the start of the experiments, while exotic tree species were eliminated. Over a period of 12 years AF was more profitable than SC due to the production of a diversity of agricultural goods, despite somewhat higher establishment costs. Other ecosystem services delivered by AF, such as biodiversity and cultural services are currently not valorized. Payment schemes for environmental services could further improve the economic benefits of AF for family farmers and alleviate establishment and learning cost

Investigation of the effect of weak non-linearities on P1dB and efficiency of class B/J/J* amplifiers

The variation of phase of the current through the non-linear intrinsic capacitances of a high-power RF device caused by the variation of the phase in the continuum of drain voltage waveforms in Class B/J/J* leads to a reduction of intrinsic drain current when moving from class B to class J* while the drain current increases from class B to class J. Consequently, a subset of voltage waveforms of the class B/J/J* continuum can be used to design amplifiers with higher P1dB, and efficiency at P1dB than in Class B. A simple choice of this subset is demonstrated with a 2.6GHz Class B/J/J* amplifier, achieving a P1dB of 38.1dBm and PAE at P1dB of 54.7%, the highest output power and efficiency at P1dB amongst narrowband linear amplifiers using the CGH40010 reported to date, at a comparable peak PAE of 72%

Extending the bounds of performance in E-mode p-channel GaN MOSHFETs

An investigation of the distribution of the electric field within a normally-off p-channel heterostructure field-effect transistor in GaN, explains why a high |Vth| requires a reduction of the thickness of oxide and the GaN channel layer. The trade-off between on-current |Ion| and |Vth|, responsible for the poor |ION| in E-mode devices is overcome with an additional cap AlGaN layer that modulates the electric field in itself and the oxide. A record |Ion| of 50-60 mA/mm is achieved with a |Vth| greater than |-2| V in the designed E-mode p-channel MOSHFET, which is more than double that in a conventional device

An E-mode p-channel GaN MOSHFET for a CMOS compatible PMIC

The operation principle of a low power E-mode p-channel GaN MOSHFET is explained via TCAD simulations. The challenges of achieving negative threshold voltage with the scaling of gate length are addressed by adjusting the mole fraction of an AlGaN cap layer beneath the gate. An inverter consisting of the proposed p-channel GaN MOSHFET with a gate length of 025 μm shows promise of a CMOS compatible Power Management IC in the MHz range

A p-channel GaN heterostructure tunnel FET with high ON/OFF current ratio

A novel mechanism to achieve a nonambipolar tunnel FET (TFET) is proposed in this paper. The method relies on polarization charge induced in semiconductors, such as group III nitrides, to enhance the electric field across the junction and facilitate unidirectional tunneling based on the polarity of the applied gate bias. This also enables enhanced control over the tunneling distance, reducing it significantly in comparison to a conventional TFET. The proposed p-channel device implemented in a novel vertical GaN nanowire geometry facilitates a reduction of footprint while still maintaining comparable performance to that of conventional E-mode p-channel devices in GaN. This opens up possibilities for E-mode p-channel GaN devices

An ultralow power 3-terminal memory device with write capability in the off-state

In this work, we demonstrated a room temperature fabricated ZnO/Ta 2 O 5 transistor for low power compute-in-memory application. By writing during the off-state, the device programmed for compute-in-memory shows power consumption in nW. By using variable pulse amplitudes for SET/RESET allows control of the on/off ratio of resistance states without affecting power consumption. Benchmarked against other ReRAMs the device shows a competitive 8 nJ per transition, which allows a reduction of power consumption in comparison to a filamentary device

Impact of channel thickness on the performance of an E-mode p-channel MOSHFET in GaN

Introduction of positive polarization charge by utilising an AlGaN cap layer between the gate oxide and the channel is one of the promising techniques to deplete a two-dimensional hole gas (2DHG) to achieve an E-mode p-channel GaN MOSHFET. The results from TCAD simulations indicate that the off-state leakage increases by orders of magnitude for channel layers thicker than 20 nm in this structure. Biasing the two-dimensional electron gas beneath the 2DHG helps alleviate this limitation at the cost of reducing on-current. Scaling the access regions and combining the two techniques allow maximum benefit in terms of on-state current, negative threshold voltage, and the on/off current ratio

On the Dynamic characteristics of Ferroelectric and Paraelectric FETs

We derive the necessary conditions for a steep subthreshold switching of a Paraelectric FET with gate scan frequency. Despite an absence of a two-valley energy profile, paraelectric FETs can be represented by a series R-C circuit that exhibit sub-60 mV/dec switching under dynamic conditions during the reverse sweep of the gate bias