Regular Article

Experimental investigation on On–Off current ratio behavior near onset voltage for a pentacene based organic thin film transistor

¹ EPSMS, FST Errachidia, Université Moulay Ismail ( UMI ), B.P. 509, Boutalamine, Errachidia, Morocco
² XLIM UMR 7252 - Université de Limoges/CNRS, 123 avenue Albert Thomas - 87060 Limoges Cedex, France

^* e-mail: a.elamrani@fste.umi.ac.ma

Received: 16 January 2018
Received in final form: 11 March 2018
Accepted: 28 March 2018
Published online: 8 June 2018

Abstract

The performance of a pentacene based organic thin film transistor (OTFT) with polymethylmethacrylate as a dielectric insulator and indium tin oxide based electrical gate is investigated.  On the one hand, we showed that the threshold voltage increases with gate voltage, and on the other hand that it decreases with drain voltage. Thus, we noticed that the onset voltage shifts toward positive voltage values with the drain voltage increase. In addition, threshold-onset differential voltage (TODV) is proposed as an original approach to estimate an averaged carrier density in pentacene. Indeed, a value of about 4.5 × 10¹⁶ cm⁻³ is reached at relatively high gate voltage of −50 V; this value is in good agreement with that reported in literature with other technique measurements. However, at a low applied gate voltage, the averaged pentacene carrier density remains two orders of magnitude lower; it is of about 2.8 × 10¹⁴ cm⁻³ and remains similar to that obtained from space charge limited current approach for low applied bias voltage of about 2.2 × 10¹⁴ cm⁻³. Furthermore, high I_On/I_Off and I_On/I_Onset current ratios of 5 × 10⁶ and 7.5 × 10⁷ are reported for lower drain voltage, respectively. The investigated OTFTs also showed good electrical performance including carrier mobility increasing with gate voltage; mobility values of 4.5 × 10⁻² cm² V⁻¹ s⁻¹ and of 4.25 × 10⁻² cm² V⁻¹ s⁻¹ are reached for linear and saturation regimes, respectively. These results remain enough interesting since current modulation ratio exceeds a value of 10⁷ that is a quite important requirement than high mobility for some particular logic gate applications.