Separation of bias stress degradation between insulator and semiconductor carrier trapping in organic thin-film transistors

Abstract

Organic thin-film transistors (OTFTs) are studied intensively for realizing practical applications of flexible or large-area circuits, but rapid degradation of OTFTs due to stress voltage or reaction with water vapor or oxygen in the air limits their lifetime. In order to analyze the cause of rapid bias-stress degradation, we propose a method that separates the cause of threshold voltage (V th) shift into insulator carrier trapping (ICT) and semiconductor carrier trapping components. The experimental results show that the ICT components account for nearly 50% of the total V th shift in n-type OTFTs, while the ICT-induced V th shifts is about 20% of the total V th shift in p-type OTFTs regardless of the insulator materials: SAM or parylene. The experimental results suggest that the short lifetime of the n-type OTFTs with SAM-based insulator is caused by the instability of the SAM-based insulator due to ICT. In addition, the instability of the p-type OTFTs with SAM-based insulator is discussed based on measurement, and as a result, capacitance shift due to ICT may also affect the degradation of highly biased p-type OTFTs.

Robustness of organic physically unclonable function with buskeeper circuit for flexible security devices

“…This phenomenon can derive from another source like bias stress degradation. 28,29) In this study, the thin CYTOP layer does not suppress phase transitions. Therefore, the thermal stability of the organic buskeeper PUF is considered from another property such as low gas permittivity.…”

Aging-robust amplifier composed of p-type low voltage OTFT and organic semiconductor load

“…Another factor is the reaction of the organic semiconductors with oxygen and moisture in the atmosphere. 23) This degradation can be suppressed by covering the entire chip with a polymerinsulating film, such as Parylene. In our test chip fabrication, the entire chip is encapsulated with a Parylene film, except for the metal-pad regions that require probe contact for measurements.…”

“…(2) The second constraint is to design circuits preferably using p-type transistors rather than n-type transistors, as the latter are less stable and lower in performance. 23) The inverter circuit can also satisfy this requirement. As shown in Figs.…”

“…Using an OTFT in a normal atmosphere degrades the transistor performance. 22,23) The transfer characteristics of the inverter change accordingly. In such situations, if a constant bias voltage is continuously applied, amplification is no longer possible, as shown in Fig.…”

“…The duration of 50 min was determined according to the experimental results of Ref. 23, in which the degradation of the OTFT was reported as being relatively fast for the initial 2000 s after the bias stress application, and then significantly slowing down after that. Thus, 50 min operation is sufficient to assess the robustness of the circuit.…”