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-µW 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.Peer ReviewedPostprint (author's final draft

Projecto e optimização da alimentação de um sensor de velocidade de onda de pulso

Dissertação para obtenção do Grau de Mestre em Engenharia Electrotécnica e de ComputadoresActualmente, a energia fornecida aos equipamentos portáteis e autónomos advém exclusivamente das baterias. Infelizmente, a manutenção de tais fontes de energia apresenta-se desvantajosa, principalmente devido à frequente recarga e manutenção necessárias. Normalmente, as baterias introduzem peso extra e volume aos equipamentos electrónicos, limitando a sua autonomia. Por outro lado, a possibilidade de recolha de energia do ambiente (Energy Harvesting) apresenta-se como uma possível alternativa às baterias, quer na sua manutenção, ou substituição. Para o caso dos equipamentos médicos especialmente incorporados no corpo humano, existe a possibilidade de recolher e armazenar energia gerada durante as actividades diárias efectuadas pelo paciente. A recolha de energia através do corpo humano, ou do meio ambiente requer determinada tecnologia e materiais específicos. Os circuitos electrónicos usados devem apresentar alta eficiência, tanto na conversão de energia, como no consumo desta. O trabalho realizado consiste na implementação de um sensor fotopletismográfico para a determinação da Velocidade de Onda de Pulso (VOP), sendo o circuito projectado de modo a optimizar o consumo energético global. Foram obtidos os valores energéticos de todos os módulos que constituem o sensor de modo a avaliar a possibilidade de alimentação através de pilhas e supercondensadores. A alimentação através da energia recolhida pelo corpo humano também foi considerada, tendo sido realizadas experiências na recolha de energia através de saltos efectuados por uma pessoa, bem como a recolha de energia através da expansão toráxica durante a respiração do humano. Um circuito composto por um conversor Buck foi testado, de modo a fornecer uma tensão fixa à sua saída com base na energia gerada através da expansão toráxica. As experiências realizadas utilizam transdutores baseados no efeito piezoeléctrico. A realização desta dissertação permitiu uma apresentação oral intitulada “Energy Harvesting and the Human Health”, na 1ª Conferência Internacional “Education, Science, Innovations” da European University, (Bulgária, Junho 2011), bem como a submissão de dois artigos: um com o mesmo título da apresentação oral, e outro com o título “Energy Harvested from Respiratory Effort”

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

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.Postprint (published version

TFET-Based power management circuit for RF energy harvesting

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%.Postprint (author's final draft

Tunnel FET device characteristics for RF energy harvesting passive rectifiers

The lack of high power conversion efficiency in RF passive rectifier circuits at sub-µW power levels with current MOSFET technologies is directly related with the difficulty of the transistors in conducting the required level of current at low voltage values. With a different carrier injection mechanism, the superior electrical characteristics of the Tunnel FET devices at low voltage values (sub-0.25 V) can outperform the process of energy conversion at ultra-low power, thus improving the operation range of RF energy harvesting circuits. In this work, a simulation study on the doping profile and material selection of Tunnel FET devices shows the impact of device properties in rectifier circuit efficiency.Postprint (published version

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

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 %.Postprint (published version

Tunnel FET device characteristics for RF energy harvesting passive rectifiers

The lack of high power conversion efficiency in RF passive rectifier circuits at sub-µW power levels with current MOSFET technologies is directly related with the difficulty of the transistors in conducting the required level of current at low voltage values. With a different carrier injection mechanism, the superior electrical characteristics of the Tunnel FET devices at low voltage values (sub-0.25 V) can outperform the process of energy conversion at ultra-low power, thus improving the operation range of RF energy harvesting circuits. In this work, a simulation study on the doping profile and material selection of Tunnel FET devices shows the impact of device properties in rectifier circuit efficiency

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 (¿T < 3 ºC) when considering a thermo-electric energy harvesting source (with a = 80 mV/K). At higher ¿T, the conversion process is degraded with the increase of the transistor losses. Considering a ¿T of 1 ºC (2 ºC), 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.Postprint (published version

Novel UHF passive rectifier with tunnel FET devices

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

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-µW 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.Peer Reviewe