Year: 2007
Type: dissertation
Abstract: Ion-sensitive field-effect transistors (ISFETs) are employed as bioelectronic sensors for the cell-transistor coupling and for the detection of DNA sequences. For these applications, thermally grown SiO$_{2}$ films are used as standard gate dielectric. In the first part of this dissertation, the suitability of high-k dielectrics was studied to increase the gate capacitance and hence the signal-to-noise ratio of bioelectronic ISFETs: Upon culturing primary rat neurons on the corresponding high-k dielectrics, $Al_{2}O_{3}$, yttria stabilised zirkonia (YSZ), DyScO$_{3}$, CeO$_{2}$, LaAlO$_{3}$, GdScO$_{3}$ and LaScO$_{3}$ proved to be biocompatible substrates. Comprehensive electrical and electrochemical current-voltage measurements and capacitance-voltage measurements were performed for the determination of the dielectric properties of the high-k dielectrics. High dielectric constants of the produced $Al_{2}O_{3}$, YSZ und DyScO$_{3}$ films facilitated the processingof ISFETs with considerably higher input capacitances than the standard SiO$_{2}$ ISFETs. The achieved breakdown fields of the $Al_{2}O_{3}$, YSZ und DyScO$_{3}$ films ensured their reliable employment as ISFET gate dielectric. Good stability against electrostatic charging and small interface state densities were concluded from small hysteresis in the capacitancevoltage measurements. In the second part of the dissertation, standard SiO$_{2}$ ISFETs with lower input capacitance and high-k dielectric $Al_{2}O_{3}$, YSZ und DyScO$_{3}$ ISFETs were comprehensively characterised and compared with each other regarding their signal-to-noise ratio, their ion sensitivity and their drift behaviour. One of the results was that the transconductance and the signal-to-noise ratio of the high-k ISFETs did not improve according to their higher input capacitance. It is assumed that high source and drain feed line resistances and the invalidity of the long-channel field-effect transistor equation for the employed ISFETs are the underlying reasons. The ion sensitivity measurements showed that the YSZ ISFETs were considerably more sensitive to K$^{+}$ and Na$^{+}$ ions than the SiO$_{2}$, $Al_{2}O_{3}$ und DyScO$_{3}$ ISFETs. Hence YSZ ISFETs are suited to study the impact of the ion sensitivity of the gate dielectric in the cell-transistor coupling mechanism. In long-term drift measurements, the YSZ ISFETs drifted much longer and further than the other ISFETs. Higher porosity of the YSZ films is assumed as underlying reason. In the final third part of the dissertation, bioelectronic experiments were performed with the high-k ISFETs. Alternating deposition of oppositely charged polyelectrolyte layers, a model experiment for DNA detection, was successfully carried out with $Al_{2}O_{3}$ and DyScO$_{3}$ ISFETs. In first DNA detection experiments with $Al_{2}O_{3}$ ISFETs, small hybridisation signals were measured. Coupling between YSZ and DyScO$_{3}$ ISFETs and the HL-1 heart cell line was performed successfully in proof of principle experiments. The shape of the signals, which were measured from HL-1 cells with YSZ ISFETs, differed [...]
Source: JuSER (Forschungszentrum Jülich)
Authors: Dirk Borstlap, Andreas Offenhäusser
Language: English
Subfield: Electrical and Electronic Engineering
Field: Engineering
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W320749613