Search

This work analyzes the third generation BESOI MOSFET (Back-Enhanced Silicon-On-Insulator Metal-Oxide-Semiconductor Field-Effect-transistor) built on UTBB (Ultra-Thin Body and Buried Oxide), comparing it to the BESOI with thick buried oxide (first generation). The stronger coupling between front and back interfaces of the UTBB BESOI device improves in 67% the current drive, 122% the maximum transconductance and 223% the body factor. Operating with seven times lower back gate bias, the UTBB BESOI MOSFET presented more compatibility with standard SOI CMOS (Complementary MOS) technology than the BESOI with thick buried oxide.

The Back Enhance (BE) SOI MOSFET is a device whose operation can be tuned by the back gate bias (VGB), i.e., it can act as an n- or p-type MOSFET if VGB is positive or negative enough, respectively. This characteristic was explored in the bio-sensing application, in which a charge-based sensor was studied through simulation. Physical dimensions (gate and underlap lengths, gate oxide, silicon and buried oxide thicknesses) were varied in order to determine the most sensitive case. The buried oxide thickness presented highest variation in the results, showing the importance of the substrate on its operation. The biomaterial charge concentration analysis showed a better sensitivity of the device for positive charges when biased as an n-type transistor, while the p-type bias presented better sensitivity to negative charges. Thus, the versatility of the BESOI MOSFET can be used as an advantage in the field of biosensors.

The study of a dielectric-modulated biosensor built on the BESOI MOSFET structure showed a crossing point of the transfer characteristics curves for target biomaterials with different dielectric constants (CID – Current Invariant Dielectric). The CID corresponds to an insensitive region for biosensing application, although it can be interesting as a reference signal measurement. It was evaluated that this behavior arises from the threshold shift and the transconductance increase as a function of the biomaterial dielectric constant. The gate voltage at the crossing point presented higher variation as a function of the metal gate-semiconductor workfunction difference, when compared to the influence of the programming gate voltage and the gate oxide charge concentration.

In this work, an improvement of Schottky junction was performed for application in Back Enhanced BESOI MOSFET. It was observed that the formation of NiSi prior to the deposition of the aluminum on it, protects the Schottky junction from the aluminum interaction with Ni during thermal treatment. As a result, the Schottky junction obtained with this new process fabrication presents a better electrical behavior with ideality factor, n, close to 1 (n = 1.02 for Werner method and n = 0.95 for Gromov method) and Schottky barrier height, Φ b = 0.42 eV.

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.

Nanoribbons built on gateless (GL) Ultra-Thin Body and Buried Oxide (UTBB) Back Enhanced SOI (BESOI) pMOSFET were analyzed as a charge-based (CB) biosensor for positive and negative charges into the biomaterial for the first time. Experimental GL BESOI pMOSFET was used as the basic structure for the CB biosensor and the influence of the charges were studied by numerical simulations. In general, when the CB biosensor was biased at weak inversion, the sensitivity is higher than when it was biased at strong inversion. For negative charges in the biomaterial, the conduction at front interface is favored. On the other hand, the conduction at back interface is higher if the biomaterial has positive charges. The nanoribbon GL UTBB BESOI pMOSFET showed to be a promising structure for an integrated charged based biosensor.

Nanoribbons built on gateless (GL) Ultra-Thin Body and Buried Oxide (UTBB) Back Enhanced SOI (BESOI) pMOSFET are analyzed as a charge-based (CB) biosensor for different sensing materials and device’s dimensions. Experimental GL UTBB BESOI pMOSFET are used as a reference structure for the CB biosensor and the influence of different materials and the device’s dimensions are studied by numerical simulations. CB biosensor presents higher sensitivities in weak inversion and for negative charges in the front gate oxide once that, for negative charges, the conduction at the front interface in BESOI pMOSFET is favored. An optimization is performed for negative charges and devices with thicker buried oxide (tBOX = 50 nm) and silicon channel (tSi = 20 nm) are more sensitive, improving the BESOI biosensor’s sensitivity in 14% in weak inversion. The improvement in strong inversion is higher (38%) but the absolute value is three times lower. The nanoribbon GL BESOI pMOSFET showed to be a promising structure for an integrated charged based biosensor, which can be easily fabricated in conjunction with the signal processing circuit.

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 third generation BESOI MOSFET (Back-Enhanced Silicon-On-Insulator Metal-Oxide-Semiconductor Field-Effect-transistor) on UTBB (Ultra-Thin Body and Buried Oxide) was fabricated, analyzed and compared to the BESOI with thick buried oxide (first generation). The stronger coupling between front and back interfaces for UTBB BESOI devices improves most of the parameters analyzed. Its higher drain current (67%), maximum transconductance (122%) and body factor (217%) with seven times lower back gate bias make the UTBB BESOI MOSFET more compatible with standard SOI CMOS (Complementary MOS) technology than the BESOI with thick buried oxide.

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 explores for the first time how the electrical characteristic of the BE (Back Enhanced) SOI MOSFETs (n-and p-type) is affected by the introduction of materials with different permittivities, aiming the biological sensing application. The BE SOI MOSFET is a planar undoped SOI device whose working principle is based on the electrical field interaction between the substrate and the front gate. The biomaterial is deposited on the underlap region between source/drain and gate to be sensed. Simulations of the BE SOI were performed using the experimental data. In the dimensions studied range, the best biosensor sensitivities as a function of the relative permittivity are obtained for the thinnest silicon film (5nm) and shortest underlap length (100nm). Other parameters influence on sensitivities like front and back gate oxide thicknesses and transistor channel dimensions are negligible.

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 presents for the first time the influence of ultraviolet (UV) light on BE SOI MOSFET. This new device from University of Sao Paulo has a reconfigurable behavior (can work as nMOS or pMOS depending of the back-gate voltage) and a very simple fabrication process, without any intentional doping steps. Aiming to build a light sensor that can be integrated on commercial SOI technologies, this paper will explore the sensitivity of the BE SOI in both operation modes, i.e., p- and ntypes, using experimental and simulated data. The best UV light sensitivity was obtained for a UV-A range (around 400nm wavelength) thanks to the front interface current increment.

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.

The aim of this work is to investigate the working principle of the new Back Enhanced (BE) SOI MOSFET, under non-conventional bias conditions. This planar BE SOI device with undoped source/drain/channel structure presents the advantage to have very simple fabrication process (without any implantation and electron beam lithography) and can act like a p- or n-type MOS, depending on the back-gate bias condition. Under non-conventional bias condition, many electrical parameters present different behavior. The threshold voltage increases linearly with the drain to source voltage (V DS ) if V DS > 0 and it is constant if V DS DS if it is negative and it is constant if V DS >0 in case of a n-type BE SOI MOSFET. This fact is explained through experimental and simulated data.

This paper reports for the first time the behavior of the new BE SOI pMOSFET at high temperatures up to 125°C. In spite of the conduction mechanism takes place at the back interface in this device, it was obtained an increase of the threshold voltage (up to 1.5 mV/ °C) and a decrease of the transconductance (c-factor up to 1.3) with the temperature increase, which is stronger than the observed for the conventional FD SOI MOSFET. The zero-temperature coefficient (ZTC) was also observed. Furthermore, a simple model was applied to calculate the ZTC bias point, and the model presents a good agreement with experimental data. The body factor is almost negligible within this temperature and the subthreshold slope presents a strong degradation at high temperature.