1688 IEEE TRANSACTIONS ON ELECTRON DEVICES, VOL. 48, NO. 8, AUGUST 2001 Low-Frequency Noise in Polymer Transistors M. Jamal Deen, Senior Member, IEEE, Ognian Marinov, Jianfei Yu, Steven Holdcroft, and W. Woods Abstract—The low-frequency noise (LFN) properties of field-ef- fect transistors (FETs) using polymers as the semiconducting sub- strate material are investigated and explained in terms of the non- stationary mobility in the semiconducting polymer. In the fre- quency range kHz it was found that noise prevails over other types of LFN in these polymer FETs (PFETs). The spec- tral density of LFN of the drain current is proportional to the DC power applied to the PFETs channel, from the ohmic to the saturation modes of device operation. In addition, is affected by the carrier mobility in PFETs channel, as in organic FETs is dependent on the biasing. Thus, can have an additional sensitivity to , that is, , where . In general, the LFN of PFETs follows the relations that have been obtained for crystal and inorganic FETs with minor correction for nonstationary mobility . Index Terms— noise, characterization of parameters and modeling of FET, Hooge’s mobility fluctuation theory noise, large-area devices and sensors, low-frequency noise in semicon- ducting organic and polymer field effect transistors, low-power circuits, nonstationary carrier mobility, polymer thin film tranm- sistors, polymer transistors. I. INTRODUCTION O RGANIC- or polymer-based field-effect transistors (PFETs) have been increasingly investigated in the past ten years [1]. This is in an effort to realize inexpensive thin-film transistors (TFTs) that can be used in some niche commercial applications, such as electronic tags, drivers in active matrix displays, or for sensing applications. The use of the semiconducting polymers in “regular” inorganic circuits allows for the functional integration on single chip of a variety of sensors, which might be impossible from using only conven- tional devices, because different polymer-based compositions have significant and selective sensitivity to various physical phenomena such as light, pressure, gas concentrations, and heat. Furthermore, the technology of preparation of polymer devices is simple and can be easily added to the standard Manuscript received November 16, 2000; revised February 23, 2001. This work was supported in part by the Natural Sciences and Engineering Research Council (NSERC) of Canada through a strategic grant award. The review of this paper was arranged by Editor J. N. Hollenhorst. M. J. Deen is with the Electrical and Computer Engineering Department, Mc- Master University, Hamilton, ON, L8S 4K1 Canada, and also with the School of Engineering Science, Simon Fraser University, Vancouver, BC, V5A 1S6 Canada (e-mail: jamal@mcmaster.ca). O. Marinov is with the Electrical and Computer Engineering Department, McMaster University, Hamilton, ON, L8S 4K1 Canada. J. Yu and S. Holdcroft are with the Department of Chemistry, School of En- gineering Science, Simon Fraser University, Vancouver, BC, V5A 1S6 Canada (e-mail: holdcrof@sfu.ca). W. Woods is with the School of Engineering Science, Simon Fraser Univer- sity, Vancouver, BC, V5A 1S6 Canada. Publisher Item Identifier S 0018-9383(01)05674-X. silicon technologies, sometimes even after the fabrication and packaging of the crystal inorganic devices and circuits. To date, investigations on the origins and models for the dc characteristics, frequency response, and other electrical prop- erties of PFETs, which are required for circuit design are being carried out [1]–[4], [11]–[13]. In addition, a correlation between the technology parameters of the fabrication of these polymer- based devices and their electrical or optical characteristics is also required. This is so that calibrated models can be developed and which can be used for predictions of both their electrical and optical performance. In this paper, the low-frequency noise (LFN) properties of the polymer-based PFETs are investigated in various operating modes. This is an attempt to determine if their noise properties can be related to the known theory of the LFN in crystalline and inorganic electronic devices, or a new theory should be devel- oped. These noise properties are important if the PFET is used as the first (input) stage in the circuit, limiting the threshold of the sensitivity in the circuit design. It is also important as a tool to probe the microscopic current transport details in or- ganic devices, as the PFETs have nonstationary field-dependent mobility. In this paper, we have developed a physically-based quantitative description for the noise level in terms of the mo- bility fluctuation theory, relating the Hooge parameter to the nonstationary field-dependent mobility. II. DEVICE DETAILS AND DC CHARACTERISTICS A set of solvents and concentrations of the solvents has been used in fabrication of the PFETs in a TFT structure (Fig. 1), similar to that in [2], [4], [5], [11], and [12]. The polymer used was regioregular poly(3-hexadecylthiophene) and it was pre- pared according to the procedure described in [5]. A degener- ately-doped Si substrate served as a common gate for all TFTs on the wafer. Gold source and drain contacts were sputter-de- posited on the thermally growth SiO gate dielectric layer and then patterned using standard photolithographic processing. The polymer layer was spun onto the wafer and then it was an- nealed in vacuum or in nitrogen at temperatures between 450 and 470 K. Details of the fabrication techniques are similar to those described in [3]. Preliminary dc measurements were used to select PFETs for noise investigations. The samples used in this paper are listed in Table I. Typical dc characteristics are shown in Fig. 2, which are similar to those, which recently and independently were obtained in [11]–[13] for similar layout de- sign. Also, and similar to what was reported in [2], the measured dc characteristics varied, depending on the measurement regime and the measurement history. 0018–9383/01$10.00 © 2001 IEEE