Chemical sensitivity of an ISFET with Ta2O5 membrane in strong acid and alkaline solutions

doi:10.1016/0925-4005(91)85010-G

Sensors and Actuators B: Chemical

Volume 3, Issue 1, January 1991, Pages 75-81

https://doi.org/10.1016/0925-4005(91)85010-G Get rights and content

Abstract

A detailed study concerning the chemical sensitivity of an ISFET with a Ta₂O₅ membrane is presented. The results indicate that in the absence of alkali ions, the Ta₂O₅-ISFET has practically an ideal Nernstian pH response in a wide pH range from −7 to 13.7. A deviation from Nernstian response has been observed in electrolyte solutions containing lithium (at pH>7), sodium and potassium (at pH>12) ions. Lithium ions have the most significant effect, giving rise to a change from pH response to pLi response.

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Inkjet printed Ta<inf>2</inf>O<inf>5</inf> on a flexible substrate for capacitive pH sensing at high ionic strength
2022, Sensors and Actuators B: Chemical
Many pH sensors on the market today have specific limitations, such as the large and fragile construction of glass electrodes, or the complicated manufacturing processes of silicon-based devices including ion-sensitive field-effect transistors (ISFETs). Furthermore, most pH sensors require a stable reference electrode, which is difficult to miniaturize. In applications where the solution properties are largely understood, the use of an impedimetric sensor without a reference electrode may be sufficient, thereby simplifying the manufacturing of such sensors. In this work, inkjet printed and flash lamp annealed Ta₂O₅ on interdigitated electrodes, with an approximate sensor area of 4 mm × 4 mm, is investigated as a capacitive pH sensing layer in 0.5 M alkali chloride buffer solutions. By using the equivalent circuit of the insulator-electrolyte interface, the double layer capacitance is shown to decrease with an increase in pH within the range of pH 2 to pH 9, and agrees with prior results for anodic Ta₂O₅. When using the device as a sensor in both 0.5 M NaCl and 0.5 M LiCl aqueous solutions, the change in capacitance at 100 Hz is approximately − 110 nF/pH. Apart from pH sensing, these results may also prove informative in other applications, such as electrolytic capacitors, electrophysiology, and battery anodes in aqueous electrolyte. Moreover, the use of flexible, gold metallized polyethylene terephthalate (PET) foils as the sensor substrate potentially allows for large-scale production via roll-to-roll manufacturing, and further permits for use of the sensor in flexible applications such as goods packaging.
Reversible and high accuracy pH colorimetric sensor array based on a single acid-base indicator working in a wide pH interval
2020, Talanta
A pH colorimetric sensor array (CSA) with fast response time (<1 min) using only one acid-base indicator, Bromothymol Blue (BB), was prepared and characterized by modulating the amount, C, of the surfactant Hexadecyltrimethylammonium p-toluenesulfonate between 0 and 0.3725 g_CTApTs/g_precursor with a constant amount of the OrMoSil precursors. The effect of the C increase is a continuous acidic shift of the calibration position, i.e. a huge variation of the pK_a value of BB in the pH range 5.80-13.50. The precision error decreased with increasing C from 0.096 pH units (lower C values) to 0.023 pH units (larger C values). This result led to the development of a model to determine the number of spots with suitable C values required for having a similar value of precision in the entire working interval of the CSA. By selecting only 4 spots the precision error is < 0.100 pH units in the pH range 5.80–13.50. With 256 spots (diameter of each spot ≈ 3 mm), the model predicted an error almost constant (≈0.010) in the entire pH range.
High performance Fin-FET electrochemical sensor with high-k dielectric materials
2020, Sensors and Actuators, B: Chemical
Citation Excerpt :
Materials with better chemical performance, meaning higher intrinsic buffer capacity, while also being more resistant to dissolution in both acidic and basic conditions, have the potential to provide reliability and stability to the device. To measure the impact of the dielectric in FETs, the detection of the acidity of a solution in aqueous electrolytes (pH) has been used as a direct comparison of the performance among different oxides [30,31]. The response of the dielectric towards pH can be described using the combined Gouy-Chapman-Stern and Site-Binding (GCS-SB) models, where the GCS model describes the electrical double layer that forms at the oxide interface, and the SB model describes the grade of ionization (protonation or deprotonation) of the surface chemical groups of the dielectric barrier [32].
In this work we combine a Fin Field Effect Transistor (Fin-FET) characterised by a high height to width aspect ratio with high-k dielectric materials to study the optimized design for chemical-FETs to provide higher transconductance (and thus a better signal to noise ratio), increased dynamic range and chemical stability. We used pH sensing to verify the design. We explored the sensitivity and linearity of the response of silicon dioxide, alumina and hafnium oxide as dielectric materials sensing pH, and compared their chemical stability in different acids. The high aspect ratio fin geometry of the sensor provides high currents, as well as a planar conduction channel more reliable than traditional silicon nanowires. The hafnium oxide Fin-FET configuration performed the best delivering the most linear response both for the output and transfer characteristics, providing a wider dynamic range. Hafnium oxide also showed the best chemical stability. Thus we believe that the developed high aspect ratio Fin-FETs/high-k dielectric system can offer the best compromise of performance of FET-based sensors.
Specific and label-free immunosensing of protein-protein interactions with silicon-based immunoFETs
2019, Biosensors and Bioelectronics
The importance of specific and label-free detection of proteins via antigen-antibody interactions for the development of point-of-care testing devices has greatly influenced the search for a more accessible, sensitive, low cost and robust sensors. The vision of silicon field-effect transistor (FET)-based sensors has been an attractive venue for addressing the challenge as it potentially offers a natural path to incorporate sensors with the existing mature Complementary Metal Oxide Semiconductor (CMOS) industry; this provides a stable and reliable technology, low cost for potential disposable devices, the potential for extreme minituarization, low electronic noise levels, etc. In the current review we focus on silicon-based immunological FET (ImmunoFET) for specific and label-free sensing of proteins through antigen-antibody interactions that can potentially be incorporated into the CMOS industry; hence, immunoFETs based on nano devices (nanowire, nanobelts, carbon nanotube, etc.) are not treated here. The first part of the review provides an overview of immunoFET principles of operation and challenges involved with the realization of such devices (i.e. e.g. Debye length, surface functionalization, noise, etc.). In the second part we provide an overview of the state-of-the-art silicon-based immunoFET structures and novelty, principles of operation and sensing performance reported to date.
Atomic layer deposition of tantalum oxide thin films using the precursor tert-butylimido-tris-ethylmethylamido-tantalum and water: Process characteristics and film properties
2017, Thin Solid Films
Citation Excerpt :
Tantalum oxide (Ta2O5) is a dielectric material having a high chemical, thermal and mechanical stability, a high refractive index (~ 2.2) and a wide optical band gap (~ 4.3 eV), a high dielectric constant (22–28 for amorphous Ta2O5), low leakage currents as well as a good dielectric breakdown strength [1–3]. Due to these interesting properties, Ta2O5 thin films have been utilized for various applications, for example as corrosion resistant coatings [4,5], protective coating for sensors [6], copper diffusion barrier [7,8], antireflective coating [9], optical waveguides [10,11], ion-sensitive membranes in solid-state ion sensors [12,13], alternative gate dielectric in metal-oxide-semiconductor field-effect transistors [1,14,15] as well as in organic thin-film transistors [16], and as high-k dielectric in dynamic random access memory (DRAM) capacitors [1–3,17,18]. The deposition of Ta2O5 thin films has been realized by numerous methods such as sputtering [2,4,6,9,11,17], electro-spray deposition [7], the thermal oxidation of thin tantalum layers [2,12,13], electron-beam evaporation [9,16], chemical vapor deposition (CVD) [15,18–20], photo-CVD [21], and atomic layer deposition (ALD) [7,8,22–44].
In this work, the precursor tert-butylimido-tris-ethylmethylamido-tantalum (TBTEMT) was applied for the atomic layer deposition (ALD) of tantalum oxide (Ta₂O₅) thin films for the first time. Water was used as the second reactant. A self-limiting, and hence, ALD-like film growth was confirmed in the temperature range from 100 to 300 °C. The temperature window of this process extends from 250 to 300 °C and features a growth rate of about 0.56 Å/cycle. For lower temperatures, the growth rate increases gradually up to 0.92 Å/cycle at 100 °C. At a deposition temperature of 200 °C, the process showed perfect layer-by-layer growth with 0.64 Å/cycle and without any noticeable incubation period on both silicon with native oxide and hydrogen-terminated silicon. In addition, the conformal coating of structures with an aspect ratio of 40:1 is demonstrated as well.
According to XPS analyses, the films are oxygen rich (Ta:O ratio around 0.34 ± 0.01 for films grown at 150–300 °C) and contain a significant amount of carbon (6 ± 2 at.%) and some nitrogen (< 3 at.%). The film densities, refractive indices and dielectric constants increase with increasing deposition temperature and are as high as 8.0 ± 0.1 g/cm³, 2.25 and 31, respectively. Films grown at 200 °C are amorphous and smooth. They exhibit a film density of 7.8 ± 0.1 g/cm³, a refractive index of 2.17 (at 550 nm) and a dielectric constant of 26 ± 1. However, the films suffer from high leakage currents (> 10^− 4 A/cm²). In addition, electrical measurements revealed the formation of an interfacial layer between the Ta₂O₅ films and bare silicon. By using substrates with a thin thermally grown silicon oxide, the leakage could be reduced by three orders of magnitude.
Post-deposition annealing at 800 °C in nitrogen resulted in the crystallization of the Ta₂O₅ films, which is also accompanied by an increase in film density and refractive index. Moreover, the crystallized films exhibit an enhanced dielectric constant of 48 ± 2. Electrical measurements revealed the growth of an interfacial layer with an equivalent oxide thickness of around 2.4 nm due to the 800 °C annealing. While this interfacial layer degrades the effective permittivity of the dielectric (e.g. 20.5 ± 0.5 for a 20 nm Ta₂O₅ film), it also causes a reduction of the leakage currents by more than three orders of magnitude (e.g. to 1·10^− 7 A/cm² for a 20 nm Ta₂O₅ film).
Miniaturized metal oxide pH sensors for bacteria detection
2016, Talanta
Citation Excerpt :
However, platinum and transition metal oxides, such as iridium, ruthenium, vanadium and osmium oxides, show ionic and electronic conductivity and may be used as direct potentiometric pH sensors [14]. For instance, Ta2O5 layers show excellent pH sensitivity in a very wide pH range [22] but their utilization up to date has been mostly limited to ISFET-based sensors [23]. Miniature ISFET-based pH sensors can be applied to bacteria activity monitoring [14–17].
It is well known that the metabolic activity of some microorganisms results in changes of pH of the culture medium, a phenomenon that can be used for detection and quantification of bacteria. However, conventional glass electrodes that are commonly used for pH measurements are bulky, fragile and expensive, which hinders their application in miniaturized systems and encouraged to the search for alternatives.
In this work, two types of metal oxide pH sensors have been tested to detect the metabolic activity of the bacterium Escherichia coli (E. coli). These pH sensors were produced on silicon chips with platinum metal contacts, onto which thin layers of IrO_x or Ta₂O₅ were incorporated by two different methods (electrodeposition and e-beam sputtering, respectively). In order to facilitate measurement in small sample volumes, an Ag/AgCl pseudo-reference was also screen-printed in the chip and was assayed in parallel to an external Ag/AgCl reference electrode. As it is shown, the developed sensors generated results indistinguishable from those provided by a conventional glass pH-electrode but could be operated in significantly smaller sample volumes. After optimization of the detection conditions, the metal oxide sensors are successfully applied for detection of increasing concentrations of viable E. coli, with detection of less than 10³ cfu mL⁻¹ in undiluted culture medium in just 5 h.

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Chemical sensitivity of an ISFET with Ta2O5 membrane in strong acid and alkaline solutions

Abstract

Sensors and Actuators B

Sensors and Actuators B

Ionensensitiver Feldeffekttransistor mit Ta2O5-Schicht für den Einsatz bei pH-Messungen

VDI-Ber.

Chemical sensitivity of an ISFET with Ta₂O₅ membrane in strong acid and alkaline solutions

Ionensensitiver Feldeffekttransistor mit Ta₂O₅-Schicht für den Einsatz bei pH-Messungen