Correlation between microstructure, electronic properties and flicker noise in organic thin film transistors

Abstract

We report on observations of a correlation between the microstructure of organic thin films and their electronic properties when incorporated in field-effect transistors. We present a simple method to induce enhanced grain growth in solution-processed thin film transistors by chemical modification of the source-drain contacts. This leads to improved device performance and gives a unique thin film microstructure for fundamental studies concerning the effect of structural order on the charge transport. We demonstrate that the 1∕f flicker noise is sensitive to organic semiconductor thin film microstructure changes in the transistor channel.

Influence of string-like cooperative atomic motion on surface diffusion in the (110) interfacial region of crystalline Ni

“…It is well known that metallic films are typically "noisy", exhibiting anomalous colored noise with power law exponent α in the power spectrum describing fluctuations in various properties (particle mobility, potential energy, etc.) that is dependent on T. This noise is arguably a fundamentally limiting factor in diverse manufacturing applications involving the development of electrical devices 61 and sensors, 62 and this type of thermal noise is often found as a complication to high resolution measurement and sensing processes. While it has long been appreciated that this ubiquitous "1/ f " noise is an equilibrium, or near equilibrium, phenomenon in many condensed materials having an origin in mobility fluctuations, a general explanation of this phenomenon has remained elusive.…”

Probing stress effects in single crystal organic transistors by scanning Kelvin probe microscopy

“…The material studied here, difluoro bis(triethylsilylethynyl) anthradithiophene (diF-TESADT), is one of a number of "designer" organic materials being studied for potential use in organic based electronics. 9 Charge mobilities on the order of 0.4 cm 2 /V•s have been achieved for diF-TESADT spun-cast devices, 10 w hile charge mobilities of 6 cm 2 /V•s have been achieved for single crystal (SC) diF-TESADT OTFTs. 11 Previous studies of spun-cast OTFTs using other organic materials have reported stress effects such as a decrease in drain current and a shift in the threshold voltage (V T ) when the organic material is under an applied gate bias over a period of several hours and these bias stress effects in the linear vs. saturation regimes have been compared.…”

Remarkably low flicker noise in solution-processed organic single crystal transistors

“…The band-like carrier transport in the present single crystal form of C 8 -DNBDT-NW was unambiguously verified by the Hall effect measurements and electron spin resonance spectroscopy 33,34 . Previous studies about the 1/f noise in disordered organic semiconductors have revealed that the 1/f noise in I D originates mainly from carrier number fluctuation (δn), i.e., δI ∝ e(δn)μ [23][24][25][26] , which is referred to as McWhorter's model (see "Methods" section) 35,36 . McWhorter's model, which is widely adapted to the 1/f noise in inorganic semiconductors, accounts for carrier capture/emission processes at the transistor's gate dielectric interface and describes the resulting current fluctuations.…”

“…It has been known that the low-frequency electronic noise commonly observed in OFETs is considered to be flicker noise (1/f noise). Among various models of 1/f noise, the most common manifestation is the McWhorter's model [23][24][25][26] , that is also used to interpret 1/f noise in conventional Si metal-oxidesemiconductor (MOS) FETs 35 . McWhorter's model takes the carrier capture/ emission to the channel into account; the fluctuation of the number of carrier δn leads to current fluctuation, δI ∝ e(δn)μ.…”

“…It is known that jitter, which are variations of the edge of a digital signal from true periodicity, often impairs the bit error rate in digital logic, which becomes more predominant in nanoscale devices and sensing applications 15,16 . Recent investigations of the 1/f noise in organic field-effect transistors based on π-conjugated polymers [17][18][19] , amorphous or polycrystalline small molecules [20][21][22][23][24][25][26] were mainly focusing on device degradation under ambient and/or irradiated conditions, and on the contact resistance effect. Unfortunately, these organic compounds typically have unavoidable structural disorder and their mobility is not sufficient for high-speed circuit operation.…”