A scanning Kelvin probe study of charge trapping in zone-cast pentacene thin film transistors

Abstract

We have used scanning Kelvin probe microscopy (SKPM) as a local probe to study charge trapping in zone-cast pentacene field effect transistors on both SiO(2) and benzocyclobutene (BCB) substrates. Annealing at 130 degrees C was found to reduce the threshold voltage, susceptibility to negative gate bias stress and trapping of positive charges within single pentacene grains. We conclude that oxygen is able to penetrate and disassociatively incorporate into crystalline pentacene, chemically creating electrically active defect states. Screening of a positive gate bias caused by electron injection from Au into pentacene was directly observed with SKPM. The rate of screening was found to change significantly after annealing of the film and depended on the choice of gate dielectric.

Reliability of Organic Field‐Effect Transistors

“…In the device operated in oxygen a positive potential transient due to trapped charge appears when the device is turned off after the stress. Reproduced with permission from [13]. Copyright 2009 Institute of Physics.…”

“…Hallam et al [13] used SKPM on devices with zone-cast, solution-processed pentacene films, which exhibited large, single-crystal-like grains. The devices showed very good threshold-voltage stability when the pentacene films were deposited on a BCB gate dielectric and were annealed at 130 8C.…”

Influence of film structure and light on charge trapping and dissipation dynamics in spun-cast organic thin-film transistors measured by scanning Kelvin probe microscopy

“…[11][12][13][14] Proximal probe techniques, such as scanning Kelvin probe microscopy (SKPM), allow us to fully explore the structure-property relationships in working OTFT structures. [14][15][16][17][18][19][20][21][22][23][24][25] SKPM provides the ability to monitor changes in charge transport phenomena in both space and time, a capability not afforded by traditional electrical performance measurements a Author to whom correspondence should be addressed. Electronic mail: lucile.teague@srnl.doe.gov alone.…”

“…SKPM imaging of active devices was accomplished using the SKPM mode of a Park XE-70 AFM (Park Systems, Inc.). 21 The time-dependent evolution of the trapped charge and its subsequent dissipation 14 were imaged by scanning the same line in the device channel repeatedly (~1 Hz scan rate) in SKPM mode. All devices were stored in a vaccum dessicator when not in use.…”

Local Charge Trapping in Conjugated Polymers Resolved by Scanning Kelvin Probe Microscopy

“…We note that our experiments were performed after several days in UHV where we would expect most volatile, not chemically bonded impurities such as water to be removed from the film. 19 An alternative explanation might be that the different electronic structure in the grain boundary region is not directly responsible for the trapping of charge, but causes the rate of injection into an otherwise homogeneously distributed trap state at the SiO 2 interface to be higher than that in the crystalline ribbons.…”