Contents lists available at ScienceDirect Microelectronics Reliability journal homepage: www.elsevier.com/locate/microrel Stability of pentacene-based top gate thin film transistor with thick parylene as dielectric under humid environment Abdou Karim Diallo a, ⁎ , Mané Seck a , El Hadji Babacar Ly a , Mohsen Erouel b , Diene Ndiaye a a Département de Physique Appliquée, UFR des Sciences Appliquées et de Technologies, Université Gaston Berger, BP. 234, Saint Louis, Senegal b Département de Physique, LaPhyMNE Faculté des Sciences de Gabès, Cité Erridah, 6072 Gabès, Tunisie ARTICLE INFO Keywords: Top gate Parylene Organic transistor Humidity Stability ABSTRACT This study presents the influence of humidity effect in top gate transistors using pentacene as active layer. The devices are made on a planarized kapton substrate, and 1 μm thick parylene has been used both as gate dielectric and encapsulating layer. Two series of measurement conditions have been used. First, the humidity rate was varied from 0 to 90% in a cell by setting exposure times of 15 min and device characterized, followed to 15 min vacuum. Secondly, humidity rate is fixed at 90% during 144 min and the electrical characteristics recorded successively. The main electrical parameters such as threshold voltage (V T ), mobility (μ), on-current (I on ), de- pletion current (I off ) and subthreshold slope (S) have been investigated. The results showed that only the electrical parameters in subthreshold region have been affected at different relative humidity (RH) levels for the first series. Under vacuum, the device exhibited stable electrical performances whereas in RH ranging from 24% to 90% we observe an increase of depletion current, and this I off increase was found to be reversible. After exposing the device with 90% of RH (second series), from 0 to 108 min in humid environment, threshold voltage, I on current, V T and charge carrier mobility remain unchanged while I off and S are highly affected. Beyond 108 min, I off current keeps increasing with a noticeable I on current degradation. Two effects have to be taken into account: (i) I off current increase without any change in on-state regime is the consequence of cumulative effect of current leakage increase in the parylene dielectric accompanied and electrical conductivity increase in penta- cene semiconductor, (ii) I on current decrease is the consequence of absorbed water molecule diffusing and in- teracting with pentacene. All these parameters are reversible under vacuum after pumping down. 1. Introduction Organic transistors have attracted attention in recent years since they offer a promising technology for low cost and large area electronic applications. The considerable development of organic field effect transistors (OFETs) enables to consider applications in fields such as flat display driving, radio frequency identification (RFID) tag and sensors [1–5]. Most of applications using organic transistors are based on bottom gate devices in which the organic semiconductor (OSC) is classically deposited onto the gate dielectric. Top gate devices are much less de- veloped. Nevertheless some applications require top gated devices. For instance, ion sensitive OFETs (IS-OFETs) need to be in top gate con- figuration in order to enable charge modulation in the channel con- secutively to ionic interaction of the dielectric surface with the liquid to analyse. One major drawback of the top gate geometry is the tricky issue of dielectric deposition on the OSC which, excluding some cases, severely damages the underlying OSC and reduces the electrical device performances. Few works using top gate configuration have been re- ported such as dielectric lamination [6], parylene dielectric [7,8] and inorganic material depositions [9], and CYTOP dielectric [10,11], and so on. Furthermore, the device instabilities in organic transistors are also a major challenge that must be pointed out in order to make this inter- esting technology reliable. The electrical parameters are degraded when exposed to bias stress or humid environment. This latter has been largely studied mostly in bottom gate configuration, in which chemical species such as water molecules interact directly with organic active layer, paving the way in some cases for chemical sensors where the detection is mainly ascribed to the change of field effect mobility, threshold voltage and/or I on /I off ratio. For instance, humidity sensors have been reported by several authors [12–16], and their applications could be found in medical and food science, cryogenic process, clean room or glove box, detection of trace moisture, and the same https://doi.org/10.1016/j.microrel.2019.113510 Received 15 October 2018; Received in revised form 21 January 2019; Accepted 30 September 2019 ⁎ Corresponding author. E-mail address: abdou-karim.diallo@ugb.edu.sn (A.K. Diallo). Microelectronics Reliability 103 (2019) 113510 0026-2714/ © 2019 Published by Elsevier Ltd. T