Sensitivity Enhancement Mechanisms in Textured Dielectric based Electrolyte-Insulator-Semiconductor (EIS) Sensors

Abstract

The possible mechanisms governing the enhancement of sensitivities of Electrolyte-insulator-semiconductor (EIS) devices upon surface modification (texturing) realized by electrostatic attachment of silica particles using 3-aminopropyl triethoxysilane (APTES) as a linker are presented. EIS devices were fabricated with a textured dielectric surface using SiO 2 particles (of diameters 475, 135, and 70 nm) and screen printed Ag/AgCl electrodes. A maximum pH sensitivity of 52.4 mV/pH was achieved for the EIS device textured with 70 nm particle size while the sensitivity with the planar dielectric was 37.1 mV/pH. The APTES modification enhanced the adsorption of H + ions by protonation of the -NH 2 to -NH 3 + sites as seen from the capacitance versus voltage (C-V) hysteresis voltages. UV-Vis absorption and photoluminescence (PL) spectra indicated that the surface defects on the textured surface increased with decreasing particle size. Zeta potential measurements suggested a combined acid-base behavior of textured surface with the formation of -NH Electrolyte-insulator-semiconductor (EIS) based sensors are advantageous because of their small size, potential for mass production at low cost and easy integration with other silicon devices. The working principle is based on the MOS device with the electrolyte replacing the metal. Chemical sensitivity is an important performance parameter and is defined as the change in potential at the insulatorelectrolyte interface occurring with the change in the pH of the electrolyte. To improve the sensitivity, various high-K dielectric materials (such as Si 3 N 4 , Al 2 O 3 , Ta 2 O 5 , Gd 2 O 3 , Pr 2 O 3 , TiO 2 , Er 2 O 3 , Sm 2 O 3 and HoTiO 3 ) have been used to enhance the field effect interaction and the buffer capacity of the insulator. Also, their stack reduces the interface defects between the semiconductor and the insulator. 1-8The surface modification is another way by which the sensitivity can be improved. For example, Cheng et al. 9 used hydroxylated surface modified with 3-aminopropyl triethoxysilane (APTES) to show slight enhancement in the pH sensitivity and attributed the changes to the added contribution of the -NH 2 groups having higher proton affinity with improved signal-to-noise ratio. He et al.10 observed a linear pH response with the combined acidic and basic characteristics of -NH 2 and -SiOH groups on the APTES modified ZnS/silica nanocable field effect transistor. Hsu et al.11 designed a glucose sensor based on a poly-silicon wire coated with a mixture of γ-APTES and silica nanoparticles (NPs). The improved detection limit was attributed to the large specific surface area of the silica NPs cluster and the increased amount of OH-bonds. Wu et al.12 fabricated a label free DNA detection device with sensitivity in the range 1 fM-10 μM by utilizing a mixture of UV illuminated γ-APTES and silica NPs. Further, Oh et al. 13 used silicon nanowires and improved the pH sensitivity from 54.9 mV/pH to 60.2 mV/pH. Xue et al.14 fabricated a Si/SiO 2 thin-film based ion-se...

Change in spectral properties of dyes upon immobilization on silicon surfaces: a combined theoretical and experimental study

“…The peaks observed in both the experimental spectra in the range of 320-325 nm, arises due to aliphatic amine, present in the linkers, which is also reported by Kumar et al [46]. The peak around 230-240 nm could be due paramagnetic defects on silicon surface as reported by Rahman et al [47] and Kumar et al [46]. To determine whether presence of another dye molecule in the neighbourhood affects the spectra, theoretical calculations were carried out with two immobilized dye molecules in close proximity, for both the linkers.…”

“…Some of these groups react with the dye molecules while others remain free, and the peak in the experimental spectra in the range of 320-325 nm is attributed to these free aliphatic amine groups. The peaks observed in both the experimental spectra in the range of 320-325 nm, arises due to aliphatic amine, present in the linkers, which is also reported by Kumar et al [46]. The peak around 230-240 nm could be due paramagnetic defects on silicon surface as reported by Rahman et al [47] and Kumar et al [46].…”

Low temperature annealed amorphous indium gallium zinc oxide (a-IGZO) as a pH sensitive layer for applications in field effect based sensors

“…Similar trends of decreased sensitivity were observed by Yang et al 10 The measured hysteresis and drift values for all three devices were found to be 1-2mV and ∼15mV/h, respectively, when measured by process described elsewhere. 13 The obtained drift rate was on higher side as reported elsewhere 10 and needs to be improved. The material used in this work (a-IGZO) requires a lower processing (or annealing) temperature (< 500 o C) than the conventional high-k dielectrics where high temperature annealing is required to obtain better sensing characteristics.…”

“…For the integrated Ag/AgCl electrode, first a 100 nm gold layer was deposited on second step of reservoir using the shadow mask with opening 10mm (L) x 0.5 mm (W). Then Ag/AgCl ink (purchased from ALS Japan) was screen printed on the gold electrode using a mask with an opening 6mm (L) x 1.0 mm (W), and dried in an oven for 3 minutes at 120 o C. 13 Schematic of the fabricated EIS device is shown in figure 1.…”

Molecular dynamics simulation of potentiometric sensor response: the effect of biomolecules, surface morphology and surface charge

“…Nonetheless, some experiments suggest that amorphous surfaces are beneficial to pH sensor response: for example, sputtered silica was shown to have a higher pH sensitivity than thermally grown silica, 89 the addition of nanowires to a planar Al 2 O 3 /SiO 2 surface increased pH sensitivity by 5 mV per pH (55 mV per pH to 60 mV per pH), 90 and texturing a silanised silica surface with silanised silica nanoparticles increased pH sensitivity by 11 mV per pH (43 mV per pH to 54 mV per pH). 91,92 However, other experiments have shown no effect of increased surface porosity on pH sensitivity, but it did show an increase in capacitance. 93,94 It is clear that further work is needed to clarify the precise relationship between surface morphology and pH sensitivity.…”