Compact modeling of optically gated carbon nanotube field effect transistor

Abstract

BackgroundCarbon Nanotube Field Effect Transistors (CNTFETs) have high charge sensitivity at room temperature [1]. By using this sensitivity, some nonvolatile memory devices have been demonstrated with charge trapping in SiO 2 gate insulator [2,3]. Besides, a new design of synapse-like circuit requires a multi-level nonvolatile memory [4]. For this application, and according to its high charge sensitivity, Optically-Gated Carbon Nanotube Field Effect Transistor (OG-CNTFET) appears as a good candidate thanks to optical writing and electrical erasing abilities both with single and multiple drain current levels [5,6].By coating a thin layer of photosensitive polymer such as poly3-octylthiophene-2,5-diyl (P3OT) over the nanotube, a CNTFET becomes an OG-CNTFET [5], as presented in Fig. 1a. Compared to the conventional CNTFET, the OG-CNTFET reveals a significant increase of the drain current below the threshold gate bias voltage. If this device is under significant powerful illumination, the gate bias will no longer control the conductivity of the CNT channel, and the optical gate will dominate the functionality. This property of variable conductance is of particular interest for neural network designs to define a third logic level. In this work, we present a compact model for OG-CNTFET. Indeed, compact modeling (i.e. SPICE-like) is a key issue for predicting the ultimate performances of these novel nano-devices in a circuit environment using standard simulation tools.Electron trapping/releasing mechanism When a thin film of P3OT coats on a CNTFET, this polymer acts as a p-type doping under no illumination condition [5]. We suppose that the CNT channel is electrostatically doped due to negative charges trapped at the polymer/SiO 2 interface in the nanotube vicinity [1].When an OG-CNTFET is under illumination with a wavelength that can be absorbed by the polymer, electron-hole pairs are generated in the P3OT layer, and a minor part of them can be separated [7]. This polymer is known for trapping only electrons [8]. If the gate is biased positively, these trapped electrons can be homogenously attracted by the electrostatic field to the P3OT/SiO 2 interface. The resulting charge density contributes to modulate the channel conductivity by screening the back gate bias. Fig. 1b describes this so-called optical gating effect. When the light is turned off, the trapped electrons are not released immediately; they are hold for about ten hours [5,7].The optical gating effect can be removed more rapidly by applying a negative gate voltage or a positive drain-source one [5-6, 9]. The negative gate bias provides an electrostatic field that contributes to release the trapped electrons at the P3OT/SiO 2 interface. Concerning the effect of the positive V ds , we assume that it creates an electric field close to the drain electrode that contributes to sweep away the trapped carriers according to the field magnitude distribution as a function of the distance to the drain electrode (c.f. Fig. 1c). Modeling of OG-CNTFETSince the OG-CNTFET...

A new repeatable, optical writing and electrical erasing device based on photochromism and electrochromism of viologen

“…Macchione [23][24][25] reported a laser-writable and electrically erasable organic photoelectrochromic device based on methylene blue, which can change its color from blue to transparent on absorption of red He-Ne laser light and return to blue when induced by an external voltage. Liao [26] constructed a compact model of an optically gated carbon nanotube field effect transistor, which can perform reversible optical writing and electrical erasing operations. Furthermore, Hu [27] proposed a novel NIR light writing and electrical erasing device based on a SWNT-PDMS/Ni-PDMS composite bilayer.…”

Design of a Polymer–Carbon Nanohybrid Junction by Interface Modeling for Efficient Printed Transistors

“…5À10 In particular, single-walled carbon nanotubes (SWNTs) have emerged as highly promising components of electronic and energy devices because of their high intrinsic charge-carrier mobility, high aspect ratio, and superior mechanical properties. 11À15 PSCs with SWNTs compose a promising heterostructure and were recently reported as a new platform for the next generation of optoelectronic devices, such as transistors, 16,17 photovoltaics, 18À20 photodetectors, 21 memories, 22 and sensors. 23 Several groups have demonstrated that thin film transistors (TFTs) and photovoltaics with a PSC/SWNT heterostructure as the channel material have improved the charge-carrier mobility and on-current.…”

“…Printable polymer semiconductors (PSCs) have attracted considerable attention because of their potential applications in large-area, low-cost, flexible, and printed optoelectronics. − However, the charge-carrier mobilities of PSC-based devices fabricated by inkjet printing are generally limited by hopping transport (lower conductivity) between polymer chains in disordered regions of such films. Therefore, the use of complementary heterostructures based on organic and inorganic semiconductors has been suggested as a potentially effective way to manipulate the optoelectronic properties of printed devices, as they may combine the desirable characteristics of both materials. − In particular, single-walled carbon nanotubes (SWNTs) have emerged as highly promising components of electronic and energy devices because of their high intrinsic charge-carrier mobility, high aspect ratio, and superior mechanical properties. − PSCs with SWNTs compose a promising heterostructure and were recently reported as a new platform for the next generation of optoelectronic devices, such as transistors, , photovoltaics, − photodetectors, memories, and sensors …”