Study of ^ΒΕSOI MOSFET Reconfigurable Transistor for Biosensing Application

Abstract

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.

Reconfigurable SOI-MOSFET: Past, Present and Future Applications

“…Ref. [31] studies the BE SOI RFET as a permittivity and charge-based biosensor (sub-section B) and refs. [32][33][34][35] discuss the RFET performance in a logic circuits (sub-section C) as shown below.…”

“…Two types of FET-based sensors are explored: the permittivity-based and the charge-based biosensors. [31] i. Permittivity-based sensor: as a field effect sensor, the electric permittivity of the biomaterial affects its drain current thanks to the electric field from gate electrode that reaches the gate oxide-silicon interface. The material of interest would be put on the gate insulator or in part of them, changing the effective dielectric constant (Fig.…”

“…14B), the biomaterial is placed on the underlap regions, acting on the channel by the fringing electric field of the front gate electrode (Fig. 14C) [31]. The BE SOI's sizes were optimized to improve their sensitivities (Table II).…”

“…In a structure like the one used for the permittivity-based sensor, i.e., the biomaterial is placed on the underlap regions (Fig. 15B), the BE SOI's sizes were also optimized for the highest sensitivities (Table III) [31]. The highest sensitivities were achieved for thicker tBOX (250nm), longer LUD (1m) and opposite trends for tOX and tSi when comparing N-and P-type BE SOI (N-type: tOX=5nm and tSi=20nm; P-type: tOX=20nm and tSi=5nm).…”

“…Optimized devices have W=1m , LUD=1m and tBOX=250nm for both N-and P-type devices. The other dimensions are: L=100nm, tOX=5nm, tSi=20nm for n-type and L=1m, tOX=20nm, tSi=5nm for PMOS transistor [31].…”