Effects of the alkyl chain length in phosphonic acid self-assembled monolayer gate dielectrics on the performance and stability of low-voltage organic thin-film transistors

Abstract

We have fabricated pentacene organic thin-film transistors ͑TFTs͒ using self-assembled monolayers ͑SAMs͒ based on alkyl-phosphonic acids with five different alkyl chain lengths as the gate dielectric and investigated the relationship between the SAM chain length and the electrical performance and stability of the transistors. A SAM chain length of 14 carbon atoms provides a maximum TFT mobility of 0.7 cm 2 / V s, along with an on/off current ratio greater than 10 5. We have also investigated the bias stress effect in these TFTs and found that the change in drain current is substantially less severe than in pentacene TFTs with polymer gate dielectrics.

Dry growth of n-octylphosphonic acid monolayer for low-voltage organic thin-film transistors

“…To date the self-assembled monolayers based on alkyl phosphonic acids [20][21][22][23][24][25][26][27] have been obtained by solution process only. In this paper we present that such monolayers can be prepared by dry method as well.…”

“…The study of the alkyl chain length on OTFTs showed that alkyl phosphonic acids with fewer than ten carbon atoms, assembled from solutions, form disordered monolayers [21]. This is a result of weaker cohesive interaction between molecules leading to OTFTs with high gate leakage current, e.g.…”

“…To obtain low leakage current with aluminium oxide, the oxide surface has been modified with polymer layers [16][17][18][19] or self-assembled monolayers (SAMs) [20][21][22][23][24][25][26]. Along with low leakage current density, the polymer surface yielded very low surface roughness of  0.3 nm and transistor operating voltages of about 6 to 8 V. Further reduction in OTFT operating voltages down to 3 V was achieved with SAMs.…”

An Extended-gate Type Organic FET Based Biosensor for Detecting Biogenic Amines in Aqueous Solution

“…The gate dielectric layer consisted of an aluminum-oxide layer (5 nm thick) and a tetradecylphosphonic acid (1.7 nm thick) selfaligned monolayer (SAM). 19,20 The aluminum-oxide layer was formed by treating the Al gate electrode with an oxygen plasma, using a plasma power of 300 W and treatment duration of 50 min. The SAM was formed by immersing the substrate in a 2-propanol solution of tetradecylphosphonic acid at room temperature.…”

Optimizing Pentacene Growth in Low-Voltage Organic Thin-Film Transistors Prepared by Dry Fabrication Techniques

“…To date, several groups have achieved low voltage OTFTs with high-k aluminium oxide (AlO x ) and a self-assembled monolayer (SAM) based on phosphonic acids [4][5][6][7]. Our gate dielectric consists of thin AlO x and n-octyl phosphonic acid.…”