Chia-Ming Yang

Drift and Hysteresis Effects Improved by RTA Treatment on Hafnium Oxide in pH-Sensitive Applications

Rapid thermal annealing (RTA) treatment in N 2 ambient is applied to optimize the drift and hysteresis effects of HfO 2 -based sensing membrane. The drift coefficient of the 8 nm thick HfO 2 -electrolyte-insulator-semiconductor (EIS) structure was 1.4 mV/h. After being treated with RTA at 900°C, the drift coefficient and hysteresis width of the 8 nm thick HfO 2 layer was reduced to 0.65 mV/h and 1.7 mV, respectively. For the HfO 2 -EIS structure treated with RTA at 500°C, the drift coefficient was increased to 3.25 mV/h because of the crystallization of the HfO 2 layer and was improved by 900°C annealing due to the densification of the HfO 2 layer. Therefore, the drift coefficient of the HfO 2 -EIS structure was reduced to 0.65 mV/h by RTA treatment at 900°C. With excellent pH sensitivity and stability, an HfO 2 layer with proper RTA processing can be used as pH sensing material in ion-sensitive field-effect transistor-type sensors. Moreover, to easily control capacitance-voltage measurements and automatically calculate parameters such as pH sensitivity, drift coefficient, and hysteresis width of an HfO 2 -EIS structure, a program based on LabVIEW was developed.

Optimization of urea-EnFET based on Ta2O5 layer with post annealing.

In this study, the urea-enzymatic field effect transistors (EnFETs) were investigated based on pH-ion sensitive field effect transistors (ISFETs) with tantalum pentoxide (Ta2O5) sensing membranes. In addition, a post N2 annealing was used to improve the sensing properties. At first, the pH sensitivity, hysteresis, drift, and light induced drift of the ISFETs were evaluated. After the covalent bonding process and urease immobilization, the urea sensitivity of the EnFETs were also investigated and compared with the conventional Si3N4 sensing layer. The ISFETs and EnFETs with annealed Ta2O5 sensing membranes showed the best responses, including the highest pH sensitivity (56.9 mV/pH, from pH 2 to pH 12) and also corresponded to the highest urea sensitivity (61 mV/pCurea, from 1 mM to 7.5 mM). Besides, the non-ideal factors of pH hysteresis, time drift, and light induced drift of the annealed samples were also lower than the controlled Ta2O5 and Si3N4 sensing membranes.

Thickness Effects on pH Response of HfO2 Sensing Dielectric Improved by Rapid Thermal Annealing

Hafnium oxide (HfO2) was directly deposited on silicon as a sensing dielectric by RF sputtering. This combination was proposed to replace the HfO2/SiO2 stacked structure. The characterizations of HfO2 sensing dielectrics of various thicknesses were widely investigated using post-rapid thermal annealing (RTA) treatments at various temperatures and process times. The pH sensitivity of a 30-nm-thick HfO2 sensing dielectric was 49.2 mV/pH, almost the same as the traditional HfO2/SiO2 stacked electrolyte–insulator–semiconductor (EIS) structure. The verified minimum thickness for a HfO2 sensing dielectric was 4 nm. The ion sensing performance of HfO2-EIS, pH sensitivity, and drift voltage were all improved by RTA treatment. With 900 °C RTA, pH sensitivities can be improved and approach 59.6 mV/pH for all thicknesses of HfO2 sensing dielectric. HfO2 sensing dielectrics with 900 °C RTA are verified as good hydrogen ion sensing materials.

Hysteresis effect on traps of Si3N4 sensing membranes for pH difference sensitivity

Abstract The mechanism of different pH sensitivities on single and stacked layer silicon nitride (Si3N4)-electrolyte insulator semiconductor (EIS) structures was investigated for the application of an inorganic ion sensitive field effect transistor (ISFET) and reference field effect transistor (REFET) pair. The capacitance–voltage (C–V) hysteresis effect of the EIS structures was measured. In addition, pH sensitivity was evaluated with different sweep directions and ranges of the substrate bias. Based on the hysteresis results, a pH-dependent trapping effect was found to decrease the pH sensitivity on a single Si3N4 sensing membrane EIS structure.

Immobilization of enzyme and antibody on ALD-HfO2-EIS structure by NH3 plasma treatment

Thin hafnium oxide layers deposited by an atomic layer deposition system were investigated as the sensing membrane of the electrolyte-insulator-semiconductor structure. Moreover, a post-remote NH3 plasma treatment was proposed to replace the complicated silanization procedure for enzyme immobilization. Compared to conventional methods using chemical procedures, remote NH3 plasma treatment reduces the processing steps and time. The results exhibited that urea and antigen can be successfully detected, which indicated that the immobilization process is correct.

Optimization of a PVC Membrane for Reference Field Effect Transistors.

For the miniaturization of ISFET sensing systems, the concept of a REFET with low ion sensitivity is proposed to replace the conventional reference electrodes through the arrangement of a quasi reference electrode and a differential readout circuit. In this study, an ion-unblocking membrane was used as the top layer of a REFET. To optimize the REFET performance, the influences of the silylating process, different plasticizers, and the composition of the PVC cocktails were investigated. A low sensitivity (10.4 ± 2.2 mV/pH) and high linearity (99.7 ± 0.3 %) in the range from pH 2.2 to pH 11.6 was obtained for the REFET with a 60 wt.% DNP/(DNP + PVC) membrane. To evaluate the long term stability, the drift coefficient was estimated, and for the best REFET, it was −0.74 mV/h. Two criteria for assessing the lifetime of REFETs were used, namely the increase in pH sensitivity to a value higher than 15 mV/pH and the degradation of linearity below 99 %. For the best REFET, it was approximately 15 days.

Effects of CF4 Plasma Treatment on pH and pNa Sensing Properties of Light-Addressable Potentiometric Sensor with a 2-nm-Thick Sensitive HfO2 Layer Grown by Atomic Layer Deposition

We investigated the effect of the carbon tetrafluoride (CF4) plasma treatment on pH and pNa sensing characteristics of a light-addressable potentiometric sensor (LAPS) with a 2-nm-thick HfO2 film grown by atomic layer deposition (ALD). An inorganic CF4 plasma treatment with different times was performed using plasma enhance chemical vapor deposition (PECVD). For pH detection, the pH sensitivity slightly decreased with increasing CF4 plasma time. For pNa detection, the proposed fluorinated HfO2 film on a LAPS device is sensitive to Na+ ions. The linear relationship between pNa sensitivity and plasma treatment time was observed and the highest pNa sensitivity of 33.9 mV/pNa measured from pNa 1 to pNa 3 was achieved. Compared with that of the same structure without plasma treatment, the sensitivity was improved by twofold. The response mechanism of the fluorinated HfO2 LAPS is discussed according to the chemical states determined by X-ray photoelectron spectroscopy (XPS) analysis. The analysis of F 1s, Hf 4f, and O 1s spectra gives evidence that the enhancement of pNa sensitivity is due to the high concentration of incorporated fluorine in HfO2 films by CF4 plasma surface treatment.

Light Addressable Potentiometric Sensor with Fluorine-Terminated Hafnium Oxide Layer for Sodium Detection

In this study, post-CF4 plasma surface treatment of light addressable potentiometric sensor (LAPS) with a HfO2-sensing membrane was carried out. pH sensitivity decreased but pNa sensitivity increased with fluorine incorporation. The highest pNa sensitivity was 31.8 mV/pNa, which was optimized with 3 min post CF4 plasma treatment. The results showed a high possibility for sensing sodium ions using an inorganic-sensing membrane and a fabrication process. Moreover, on the basis of the analysis of atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS) spectra, a sensing mechanism was developed.

Characterization on pH sensing performance and structural properties of gadolinium oxide post-treated by nitrogen rapid thermal annealing

A detail investigation on the pH sensing performance of Gd2O3 layer was proposed in this work. Electrolyte–insulator–semiconductor (EIS) structure with Gd2O3 layer deposited directly on silicon by reactive radio frequency sputtering with Gd target was chosen as the testing platform. The postdeposition rapid thermal annealing (RTA), performed at various temperatures for 1 min in N2 ambience, was first used to improve the pH sensing performance of Gd2O3. With RTA treatment at 800 °C, pH sensitivity of Gd2O3 EIS structure can be increased from 35.5 mV/pH to 55 mV/pH. This behavior can be explained by the increase of surface sites, which is supported by atomic force microscopy analysis. With RTA treatment at 700 °C and 800 °C, the drift coefficient for Gd2O3 layer was reduced to 0.03 and 1.2 mV/h, which is resulted from the densification of Gd2O3 layer supported by x-ray photoemission spectrometry. Therefore, Gd2O3 layer with RTA in N2 ambience at 700 °C or 800 °C could be a potential candidate for pH-sensiti...

Light-Immune pH Sensor with SiC-Based Electrolyte--Insulator--Semiconductor Structure

An electrolyte–insulator–semiconductor (EIS) structure with high-band-gap semiconductor of silicon carbide is demonstrated as a pH sensor in this report. Two different sensing membranes, i.e., gadolinium oxide (Gd2O3) and hafnium oxide (HfO2), were investigated. The HfO2 film deposited by atomic layer deposition (ALD) at low temperature shows high pH sensing properties with a sensitivity of 52.35 mV/pH and a low signal of 4.95 mV due to light interference. The EIS structures with silicon carbide can provide better visible light immunity due to its high band gap that allows pH detection in an outdoor environment without degradation of pH sensitivity.