The Motivation for and Challenges to Scaling Down Organic Field‐Effect Transistors

Abstract

v) operating frequency, [13][14][15] vi) contact resistance, [16][17][18][19] vii) crystallinity and grain boundaries of the organic thin films, [20][21][22] viii) active matrix OFET array or integrated circuit, [23][24][25][26][27][28] ix) novel deposition techniques, [29][30][31][32][33] x) unconventional substrates for OFETs, [34][35][36][37] xi) physical or biological sensors, [38][39][40][41][42][43][44] etc. The progress in all these different aspects has framed the development roadmap of the OFETs. Among all the challenges in the OFET development, some of them are more intricate than the others which deserve the research community to spend more efforts. In this review, I try to discuss the development bottlenecks or limitations in the current OFET research, especially on downsizing. I will also explore some possible direction that can lead to solutions. In the OFET development, the channel carrier mobility (μ) is always considered as the critical parameter to evaluate the overall performance of the devices. The improvement of the dielectric insulators, device structures, or crystallinity of the organic thin films is usually quantified or reflected by the improvements of the mobility values. In some commonly used organic semiconductors, such as pentacene, the variations in the reported mobility values can be up to a few orders of magnitude. Different factors such as the purification level of the semiconductors, fabrication parameters, or processing environments are believed to influence the quality of the OFET active layers and thus the channel carrier mobility. [45][46][47][48][49] Other than these physical components, the way of evaluating the carrier mobility in OFET is equally essential. Erroneous mobility would blur the physics of the device and more importantly, lead to an incorrect conclusion. In general, the carrier mobility in the linear or saturation regime is extracted from the slope of the I D versus V G or I D 1/2 versus V G plot, respectively. The region of the transfer curves used to evaluate the carrier mobility would affect the values significantly. If a kink or change of slope is present in the transfer curves due to the contact resistances, nonequilibrium biasing of shortchannel, minority carrier injection, or other device issues, overestimation of the carrier mobility would result and it has been discussed in the recent work by Gundlach and co-workers, [50] Choi et al., [51] and Okachi. [52] Although the carrier mobility is a significant performance indicator, it should not be considered as the only parameter to access the performances of the OFETs. One major barrier that limits the development of OFET is that the research community too concentrates on the carrier mobility andThe development of organic field-effect transistors (OFETs) in the past few decades has emphasized the carrier mobility of the active layer. It is true that carrier mobility is an important parameter to quantify transistor performance; however, it should not be considered as the only parameter necessary to evaluate ...

Organic Electronics Picks Up the Pace: Mask‐Less, Solution Processed Organic Transistors Operating at 160 MHz

“…Such a value of R c is not only a key requirement in order to access frequency regimes in excess of 100 MHz, [15,19] but is among the best reported values for OFETs in general and is extremely low when considering the case of transistors realized via direct-writing, solution-based methods and optimized for low geometrical overlap of electrodes and high frequency operation. [37][38][39] We then measured the AC characteristics of our device by means of S-parameters, using a setup already described in our previous work, [27] calibrated with a SOLT procedure and corrected with a 12-term error model. From the measured S-parameters, the parasitic contributions of the pads and interconnections are de-embedded from the measurement with a one-step procedure [40] and the hybrid parameter h 21 is extracted (Figure 2c), allowing to identify f t according to h 21 (f t ) = 0 dB, which yields an unprecedented f t of 160 MHz at a bias voltage of 40 V for OFETs in the case of the best device (Figure 2c, linear fit).…”

A Critical Outlook for the Pursuit of Lower Contact Resistance in Organic Transistors

“…[17] However, the contact resistance (R C ) persists as a major impediment toward further development of circuits based on organic transistors. [18][19][20][21] This is especially true for the development of organic TFTs for low-power, high-frequency applications, such as mobile activematrix displays, since a high R C limits the maximum unitycurrent-gain-cutoff (transit) frequency that would otherwise be expected through device miniaturization. [22] High contact resistance in organic TFTs continues to be a major problem despite significant strides in expanding both the breadth of To take full advantage of recent and anticipated improvements in the performance of organic semiconductors employed in organic transistors, the high contact resistance arising at the interfaces between the organic semiconductor and the source and drain contacts must be reduced significantly.…”

Stencil mask defined doctor blade printing of organic single crystal arrays for high-performance organic field-effect transistors

“…12,13 Moreover, to reach a higher level of integration, OFETs are always in an array form with high spatial resolution. 14 These applications require the precise patterning of OSC thin films. 15,16 Well-patterned OSCs can avoid unwanted leakage current, lower the off-state current and reduce crosstalk between neighboring devices.…”