Hybrid dielectrics composed of Al2O3 and phosphonic acid self-assembled monolayers for performance improvement in low voltage organic field effect transistors

Nano Convergence

Table 1 Thin film parameters of the hybrid dielectrics with PA-SAMs

Dielectric	Molecular length^a (nm)	t ^b_i (nm)	Contact angle (º)	C_i at 10 kHz (nF/cm²)	Estimated k^c
Al₂O₃	–	23	< 10	279	7.2
HPA	1	0.91	102	246	2.2
DDPA	1.74	1.59	105.5	230	2.6
ODPA	2.49	2.27	109.8	222	2.8
PHDA	2.25	2.05	25.9	223	2.6
MDPA	1.9	1.74	65.1	240	3.4
PFPA	2.24	2.04	102	234	3.3
HUPA	1.72	1.57	28.5	239	3.0

Molecular length (nm), thickness of insulator (t_i) (nm), contact angle (°), capacitive density (C_i) at 10 kHz (nF/cm²) and Estimated dielectric constant k
^a The molecular lengths of the PA-SAMs were estimated by assuming the conditions, such as the ideal bonding length and flat molecules according to the alkyl chain axis. The molecular lengths were defined as the distance between the hydrogen atom at the phosphonic acid and the opposite end atom along the alkyl chain axis
^b t_i was the thickness of each Al₂O₃ and PA-SAM layer (not hybrid dielectric). The t_i of the reference Al₂O₃ was a measured value. The t_i of the PA-SAMs were calculated by assuming the calculated molecular lengths, the tilted bonding angle to the substrate (24°) and full coverage with a high density on the substrate
^c k was the calculated dielectric constant of each Al₂O₃ and PA-SAM layer (not hybrid dielectric) using Eqs. (1) and (2)