David Cavalheiro

Pespectives of TFET devices in ultra-low power charge pumps for thermo-electric energy sources

The superior electrical characteristics of the heterojunction III-V Tunnel FET (TFET) devices can outperform current technologies in the process of energy harvesting conversion at ultra-low power supply voltage operation (sub-0.25 V). In this work, it is shown by simulations that a cross-coupled switched-capacitor topology with GaSb-InAs TFET devices present better conversion performance compared to the use of Si FinFET technology at low temperature variations (ΔT <; 3 °C) when considering a thermo-electric energy harvesting source (with α = 80 mV/K). At higher ΔT, the conversion process is degraded with the increase of the transistor losses. Considering a ΔT of 1 °C (2 °C), one cross-coupled stage with TFET devices can achieve 74 % (69 %) of power conversion efficiency when considering an output load of 0.4 μA (6 μA). At the same conditions, the FinFET charge pump is shown inefficient.

Insights Into Tunnel FET-Based Charge Pumps and Rectifiers for Energy Harvesting Applications

In this paper, the electrical characteristics of tunnel field-effect transistor (TFET) devices are explored for energy harvesting front-end circuits with ultralow power consumption. Compared with conventional thermionic technologies, the improved electrical characteristics of TFET devices are expected to increase the power conversion efficiency of front-end charge pumps and rectifiers powered at sub-

TFET-Based Power Management Circuit for RF Energy Harvesting

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Novel charge pump converter with Tunnel FET devices for ultra-low power energy harvesting sources

power levels. However, under reverse bias conditions the TFET device presents particular electrical characteristics due to its different carrier injection mechanism. In this paper, it is shown that reverse losses in TFET-based circuits can be attenuated by changing the gate-to-source voltage of reverse-biased TFETs. Therefore, in order to take full advantage of the TFETs in front-end energy harvesting circuits, different circuit approaches are required. In this paper, we propose and discuss different topologies for TFET-based charge pumps and rectifiers for energy harvesting applications.

Prospects of Tunnel FETs in the Design of Power Management Circuits for Weak Energy Harvesting DC Sources

This paper proposes a Tunnel FET (TFET)-based power management circuit (PMC) for ultra-low power RF energy harvesting applications. In contrast with conventional thermionic devices, the band-to-band tunneling mechanism of TFETs allows a better switching performance at sub-0.2 V operation. As a result, improved efficiencies in RF-powered circuits are achieved, thanks to increased rectification performance at low power levels and to the reduced energy required for a proper PMC operation. It is shown by simulations that heterojunction TFET devices designed with III-V materials can improve the rectification process at received power levels below -20 dBm (915 MHz) when compared to the application of homojunction III-V TFETs and Si FinFETs. For an available power of -25 dBm, the proposed converter is able to deliver 1.1 μW of average power (with 0.5 V) to the output load with a boost efficiency of 86%.

Novel UHF Passive Rectifier with Tunnel FET Devices

Compared to conventional technologies, the superior electrical characteristics of III-V Tunnel FET (TFET) devices can highly improve the process of energy harvesting conversion at ultra-low input voltage operation (sub-0.25V). In order to extend the input voltage/power range of operation in conventional charge pump topologies with TFET devices, it is of the major importance to reduce the band-to-band tunneling current when the transistor is under reverse bias conditions. This paper proposes a new charge pump topology with TFET devices that attenuate the reverse losses, thus improving the power conversion efficiency (PCE) in a broader range of input voltage values and output loads. It is shown by simulations that compared with the conventional gate cross-coupled charge pump and considering an input voltage of 640 mV, the proposed topology reduces the reverse losses from 19 % to 1 %, for an output current of 10 μA. For this case, the PCE increased from 63 % to 83 %.

A comparison of TFET rectifiers for RF energy harvesting applications

In this paper, a new tunnel FET (TFET)-based power management circuit (PMC) is proposed for weak dc energy harvesting sources. Thanks to their particular carrier injection mechanisms, TFETs can be used to design efficient energy harvesting circuits by enabling the power extraction from sources which are not only at very low voltage levels (sub-0.1 V) but also at very low power levels (a few nW). As TFET devices are designed as reverse-biased diodes, changes in conventional circuit topologies are required in order to take full advantage of these emerging devices. The circuit design techniques proposed in this paper represent an improvement in output voltage and input power range with respect to previously published TFET-based PMCs. Simulation results show that the TFET-based PMC can sustain itself from a 2.5 nW@50 mV dc source, powering a load at 0.5 V with 29% of efficiency.

A battery-less, self-sustaining RF energy harvesting circuit with TFETs for µW power applications

The increase of the losses in UHF passive rectifiers with Tunnel FET devices at large RF AC amplitudes are mainly due to the high reverse current inherent of this technology when subjected to high reverse bias conditions. In this work, a new UHF passive rectifier circuit is proposed, with the purpose of reducing the reverse current suffered by Tunnel FET devices at large RF AC amplitudes. Compared to the differential-drive rectifier, the proposed topology is shown to improve the output voltage and power conversion efficiency at similar RF voltage/power conditions as well as the transmission distance for RFID applications.

Tunnel FET device characteristics for RF energy harvesting passive rectifiers

In this work the performance of Tunnel FET (TFET)-based rectifiers is explored for ultra-low power applications. At a device level, when the TFET is reverse-biased its current is characterized by reverse band-to-band tunneling and drift-diffusion carrier injection mechanism. This electrical characteristic may degrade the performance of conventional TFET rectifiers due to the losses resulting from the reverse conduction of the transistors during their off state. To combat this drawback, the presented work proposes new TFET-based rectifier topologies for RF-powered energy harvesting circuits that attenuate the reverse losses suffered by the transistors. The results compare three topologies for sub-μW power levels at two frequencies of operation: 915 MHz and 100 MHz.

Ultra-Low Input Power Conversion Circuits based on Tunnel-FETs

This paper proposes a Tunnel FET (TFET) power management circuit for RF energy harvesting applications. In contrast with conventional MOSFET technologies, the improved electrical characteristics of TFETs promise a better behavior in the process of rectification and conversion at ultra-low power (μW) and voltage (sub-0.25 V) levels. RF powered systems can not only benefit from TFETs in front-end rectifiers by harvesting the surrounding energy at levels where conventional technologies cannot operate but also in the minimization of energy required by the power management circuit. In this work we present an energy harvesting circuit for RF sources designed with TFETs. The TFET controller emulates an adequate impedance at the output of the rectifier in order to allow maximum transfer of power from the RF source to the input of the boost converter. The output load is activated once the output capacitor reaches a voltage value of 0.5 V. The results show an efficiency boost of 89 % for an output load consuming 1 μW with an available RF power of -25 dBm.