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This paper reports the study of the Back Enhanced SOI (BESOI) MOSFET improvement through the inclusion of ndoped regions on the drain and source regions underlapped with the gate. This study was performed using TCAD Synopsys Sentaurus simulator. The main characteristic of the original BESOI MOSFET is the reconfigurable behavior, depending on the back-gate bias (V GB ) the device can act as a p- or n-type transistor. However, the I on current is typically asymmetric. The proposed new structure by adding n-doped regions improves the drain current when the new BESOI is in the n-type BESOI configuration, which may take both transistor types to the same current level. The best results to L MP = 1 μm was obtained for V GB = |30| V, mainly when the transistor is in the triode region.

This paper presents for the first time the BESOI (Back Enhanced SOI) MOSFET working as a charge-based BioFET sensor. The experimental device was used to calibrate the numerical simulations in order to optimize the biosensor improving its sensitivity. The biomaterial is deposited on the silicon dioxide on the underlap regions (between drain/source electrodes to front gate sidewalls) for a large range of charges concentration at the biomaterial/silicon dioxide/silicon film region. It was defined a biosensor sensitivity in order to evaluate its performance when the devices dimensions like the transistor channel (L) and underlap (L UD ) lengths, silicon film (t Si ), gate oxide (t ox ) and buried oxide (t BOX ) thicknesses were changed. The optimum charge-based BioFET sensor device based on BESOI structure was obtained for L=100nm, t BOX =250nm, L UD =1μm, t ox =5nm and t Si =20nm.

The BESOI MOSFET is a reconfigurable transistor, i.e., it can work as an n-type or a p-type device due to its back enhanced operating principle. The back gate is used to induce carriers at the back interface (silicon film/buried oxide) to the low doped channel. This work aims to propose a first order model for the drain current at linear region of the p-type BESOI MOSFET based on the back and front silicon film/SiO 2 interfaces conduction. The analytical expression takes into account the series resistance, that plays an important role in the BESOI MOSFET due to the low doped channel and the drain and source Schottky contacts. The comparison between simulated and modeled data showed a very good agreement for a first order modeling.

The BESOI (Back Enhanced SOI) MOSFET is a new device that was developed and fabricated at the University of Sao Paulo in 2015. Its main advantages are the reconfigurable behavior, i.e., can work both like P- and N-type transistor depending only of the back gate bias, and fabrication simplicity. This paper studies the influence of channel doping concentration on the sensitivity of BESOI MOSFET used as a light sensor. The light sensitivity is investigated for different doping elements (boron and phosphorus) and it is shown that one impurity is more suited for a certain operation mode, i.e., pMOS and nMOS. An optimal doping concentration for better light sensitivity is obtained, resulting in $10^{\mathbf{17}} \mathbf{cm} ^{\mathbf{-3}}$ of boron for p-type $(V_{\mathbf{GB}} \lt \lt 0)$ and the same level of phosphorus for n-type $(V_{\mathbf{GB}} \gt \gt 0)$ BESOI MOSFET.

The Back Enhanced SOI (BESOI MOSFET) is a planar reconfigurable device, which transistor type (n- or p-type) can be programed by the back-gate bias. This transistor is explored in this paper for biosensing application through numerical simulation, based on the fabricated device experimental results. The permittivity value and the charges inside the biomaterial deposited on the underlap region (between gate and source/drain contacts) influence the BESOI MOSFET drain current. The dimensions of the device were evaluated in order to optimize the sensitivity. Among the studied parameters, the underlap length was the most relevant parameter. For short underlap devices, the fringe electric field from the front gate electrode benefits the permittivity-based sensors, while long underlap length devices have a bigger sensitive area in which the charge-based sensor presented better results. Also, the n-type biased device presented higher sensitivity to positively charged materials, while the p-type biased one presented better result for negatively charged materials. The parameters optimization resulted in one order magnitude improvement of the sensitivity for the permittivity-based sensor, for both n- and p-type. As for the charge-based sensor, the optimized device presented twice as bigger sensitivity for the n-type, and at least eight times improvement for the p-type device. This fact represents an advantage of the BESOI structure as the type of the device can be chosen by the back-gate bias.

A simple model is proposed for the Back Enhanced SOI MOSFET in triode region. This model is based on a conventional MOSFET model in series with resistors and antiparallel Schottky diodes. A robust parameter extraction method, based on lateral optimization, is also presented. The dependence of the extracted parameters with the back-gate bias is studied.

This paper reports the optimization of the silicon film thickness on the Back Enhanced (BE) SOI MOSFET working as a light sensor on the visible spectrum. The BE SOI MOSFET is a kind of undoped junction-less SOI transistor, which works as an n-type or p-type MOS, depending on the back bias conditions. The BE SOI underlap regions (drain/source to gate) are used as a light sensor that can be integrated on commercial UTB (Ultra Thin Body) SOI technologies. This paper is going to explore the sensitivity of the BE SOI MOSFET as a function of the silicon thickness (from 5 to 30nm) and for wavelengths from the ultraviolet-A (UV-A, $\lambda \approx 400$ nm) to red ($\lambda \approx 635$ nm) spectra. Experimental and simulated data indicate that the optimized silicon film $\textbf{t}_{\mathbf {Si}}$textbf is 15nm, where the generation and recombination influences present the highest sensitivity for the visible spectrum.

A tradeoff between transistor reconfigurability and a Zero Temperature Coefficient (ZTC) bias point was observed and analyzed for Back Enhanced SOI (BESOI) MOSFET for the first time. The ZTC is observed only for BESOI MOS with aluminum Source/Drain (S/D) electrodes (ohmic contact with the channel) while the transistor reconfigurability is present only for BESOI MOS with nickel S/D electrodes (Schottky contact). This tradeoff is discussed and demonstrated experimentally and by numerical simulations. For ohmic S/D contacts, the temperature-independent point (ZTC) happens for front gate bias from −2.44 V to −0.61 V (for a back gate VGB changing from −15 V to −30 V respectively). Following other technologies, such as UTBB and FinFET, this point represents the compensation between the threshold voltage decrease and the mobility degradation when increasing the temperature. However, for S/D to channel Schottky contacts, there is no ZTC point and only for this condition the BESOI presents a reconfigurable behavior, i.e., p-type and n-type BESOI behavior can be observed by applying different VGB. The BESOI CMOS inverter built with nickel S/D electrodes was used to confirm the transistor reconfigurability. Therefore, depending on the S/D electrodes material, a reconfigurable device or a ZTC bias point behavior on BESOI MOSFET is observed, which is useful for different applications at the same chip.

In this work, the BE SOI MOSFET was studied for the first time as a biological material detector. This device is a planar undoped reconfigurable (i.e., it can act as an n-type or ptype) transistor, with a simple fabrication process. Numerical simulations of the drain current as a function of the front gate voltage were performed based on previous experimental results. The biological material was modeled by changing the permittivity of the dielectric on the gate underlap regions. Due to its unique operation principle, a shift on the threshold voltage was observed depending on the biological element, transistor type and charges in both oxides, front gate and buried ones. In addition, the drain current increased, mainly due to the front interface conduction. The linear behavior of the drain current as a function of the permittivity of the material indicates that the BE SOI MOSFET is a promising alternative as a biosensor.

This paper reports the temperature influence on the Back Enhanced (BE) SOI MOSFET fabricated with two different source/drain contact electrodes: Ohmic and Schottky. The BE SOI MOSFET (Patent BR 102015020974-6, 2015) is a kind of undoped junction-less SOI transistor, which works like an n-type or p-type MOS, depending on the back bias conditions. In spite of the Schottky contact at source/drain is mandatory in order to have both type of transistor working in a similar way, the use of Ohmic contact may present some specials advantages. The results showed the presence of a ZTC (Zero Temperature Coefficient) bias condition only in the device with Ohmic source/drain contact. It was observed that the Schottky contact resistance decreased when the temperature increases resulting in a higher current and consequently the absence of the ZTC. This effect is explained through experimental measurements and simulation.

This paper reports the characteristics and the operation of the new BE SOI MOSFET used to build a logic inverter for the first time. The main characteristics of this device is its simplicity of fabrication and the reconfigurable behavior, i.e, it can act as a n-type transistor or as a p-type transistor depending on the back gate bias. Furthermore, an inverter circuit was built and the static response was measured. The BE SOI inverter showed a characteristic CMOS inverter curve. Finally, the threshold voltage variation with the silicon and gate oxide thickness is explored in order to find the best inverter circuit design.