The properties of the dielectric strongly influence the performance of organic thin-film transistors. In this letter, we show experimental results that quantify the influence of the roughness of the dielectric on the mobility of pentacene transistors and discuss the cause of it. We consider the movement of charge carriers out of the "roughness valleys" or across those valleys at the dielectricsemiconductor interface as the limiting step for the roughness-dependent mobility in the transistor channel.

A main focus of research on organic semiconductors is their potential application in passive organic radio-frequency identification (RF-ID) tags. First prototypes working at 125 kHz have been shown by industrial research groups. However, to be commercially viable, the organic RF-ID tag would need to be compatible with the base-carrier frequency of 13.56 MHz (ref. 2). High-frequency operation has been out of reach for devices based on organic semiconducting material, because of the intrinsically low mobility of those materials. Here, we report on a rectifier based on a pentacene diode that can rectify an incoming a.c. signal at 50 MHz. At 14 MHz, a rectified voltage of 11 V for an a.c. voltage with a peak-to-peak amplitude of 36 V has been achieved. On the basis of those results, we estimate the frequency limits of an organic diode showing that even the ultra-high-frequency band at around 800 MHz is within reach.

The concept of noise margin is crucial in the design and operation of digital logic circuits. Analytical expressions for the transfer curves of an inverter based on two depletion-mode p-type organic thin-film transistors (OTFTs) were calculated. Based on these expressions, the values for the noise margin of organic-based inverters were calculated. In this paper, the influence of the OTFT parameters on the noise margin is presented. Knowing that statistical variations of the transistor parameters are inherent to OTFT technology, these statistical variations are also taken into account. Finally, a circuit yield analysis is presented.

In this article, we compare the direct current ͑dc͒ and high-frequency performance of two different organic diode structures, a vertical diode and an organic field effect transistor ͑OTFT͒ with shorted drain-gate contact, regarding their application in a rectifying circuit. For this purpose, we fabricated both diode structures using the organic semiconductor pentacene. dc measurements were performed showing a space-charge-limited current mobility of more than 0.1 cm 2 / V s for the vertical diode and a field effect mobility of 0.8 cm 2 / V s for the OTFT with shorted source-drain. High-frequency measurements of those diode structures in a rectifier configuration show that both types of diodes are able to follow the base-carrier frequency of 13.56 MHz which is essential for viable radio-frequency-identification ͑rf-ID͒ tags. Based on those results we evaluate the performance limits and advantages of each diode configuration regarding their application in an organic rf-ID tag.

We have developed a method for integrating n-and p-type organic thin-film transistors ͑OTFTs͒ on the same substrate. An integrated shadow mask was used for the n-and p-type semiconductor patterning. The integrated shadow mask can be aligned with submicron accuracy relative to the OTFT substrate. This allows for the integration at transistor level of n-and p-type OTFTs on the same substrate. A complementary inverter was fabricated, showing excellent performance while operating at a supply voltage of 2 V.

We have realized a light-emitting organic field-effect transistor (LEOFET). Excitons are generated at the interface of an n-type and a p-type organic semiconductor heterostructure inside the transistor channel. The dimensions and the position of the p-n heterostructure are defined by photolithography. The recombination region is several microns from the metal electrodes. Therefore, the exciton quenching probability in this device is reduced. Numerical simulations show that the recombination region can move within the transistor channel by changing the biasing conditions.

All applications of organic thin film transistors require patterning of the organic thin film to achieve a low off current and to prevent cross talk between neighboring transistors. A common method for patterning consists of using a protective layer and etching the uncovered small molecule film by oxygen plasma. One of the handicaps of this process is the observed degradation of the transistor characteristics. By varying the resist overlap, the authors show that the main cause of this performance degradation is, in fact, a far-reaching underetch of the oxygen plasma which can be overcome by choosing the right geometry of the resist pattern.

For organic thin-film transistors where source-drain contacts are defined on the gate dielectric prior to the deposition of the semiconductor (“bottom-contact” configuration), the gate dielectric is often treated with a self-assembled molecular monolayer prior to deposition of the organic semiconductor. In this letter, we describe a method to apply an ultrathin solution-processed polymer layer as surface treatment. Our method is compatible with the use of the bottom-contact configuration, despite the fact that the polymeric surface treatment does not stand a photolithographic step. Furthermore, we show that our surface treatment results in superior transistor performance.