Cheng-En Lue

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.

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.

Nano-IGZO layer for EGFET in pH sensing characteristics

In-Ga-Zn-O (IGZO) was widely applied in the substrate of TFT to replace a-Si in recent year. In this study, IGZO layer with thickness of 70 nm is first proposed as a pH sensing membrane directly on P-type Si substrate acting as an extended gate of conventional extended-gate field-effect Transistor (EGFET). Material criteria of extended gate electrode are low resistance and high capacitance. Therefore, Ar/O2 ratio was modified in the rf sputtering with IGZO target. Post deposition anneal was also performed to check the sheet resistance and pH sensing performance. EGFETs were measured in standard pH buffer solution by using B1500A and constant voltage constant current (CVCC) circuit. Similar IDS-VGS curves including transconductance (Gm) and substrate swing (S.S.) are obtained in various sputtering conditions of IGZO compared to commercial NMOSFET in CD4007. pH application range is only between pH 2 to pH 10. IGZO-EGFET prepared by Ar/O2 ambience of 24/1 in sputtering can have a sensitivity of 59.5 mV/pH. Lower sensitivity and linearity can be observed in the samples with RTA treament at higher temp and in O2 ambience. N2 anneal at 500°C can be used to improve pH sensing performance for IGZO-EGFET prepared by Ar/O2 ambience of 20/5 in sputtering. Nano-IGZO layer is verified to be the sensing membrane in EGFET to have a high sensitivity of 59.5 mV/pH for the first time. More studies on enlargement pH application range and minimization of non-ideal effect still need to be investigated.

Fluorine Incorporation and Thermal Treatment on Single and Stacked Si3N4 Membranes for ISFET/REFET Application

In this study, Si 3 N 4 -electrolyte insulator semiconductor structures based on single (Si 3 N 4 ) and stacked (SiO 2 /Si 3 N 4 ) layers were investigated. A difference in pH sensitivity between these two structures of 9.9 ± 2.0 mV/pH was observed, and this result could be applied to build an ion-sensitive field-effect transistor (ISFET)/reference field-effect transistor (REFET) pair. For further realization, the differential sensitivity was increased through some post-treatments. For the REFET application, the sensitivity of the single-layer structure can be reduced to 15.3 ± 4.5 mV/pH by rapid thermal annealing treatment. To increase the sensitivity of the stacked-layer structure, CF 4 plasma treatment was used. The highest sensitivity was 49.9 ± 0.8 mV/pH, and the differential sensitivity can be increased to 34.6 ± 5.3 mV/pH.

Differential Light Addressable Potentiometric Sensor with Poly(vinyl chloride) and HfO2 Membranes for pH Sensors

In this paper, a differential measurement setup for the light addressable potentiometric sensor (LAPS) is proposed. The LAPS with a HfO2 layer as the sensing membrane was used, and different weight percentages of DNP/(PVC+DNP) [DNP: dinonylphtalate, PVC: poly(vinyl chloride)] membrane were cast on the surface of HfO2-LAPS. The pH sensitivity can be decreased from 58.6 to 24.5 mV/pH by using 60 wt % PVC cocktail. Then, the pH sensitivity measured through a differential circuit was 30.1 mV/pH, showing high potential for replacing the function of a conventional reference electrode as an ion-sensitive field-effect transistor (ISFET)/reference field-effect transistor (REFET) pair. In addition, to confirm the output signal of the two substrate electrodes, a specific measurement setup was used.

1.2.1 Urea Biosensor Using NH3 Nitrided Amine Groups on Flexible Substrate

In this study, indium tin oxide (ITO) layers were deposited on polyethylene terephthalate (PET) substrates (ITO/PET) as a sensing membrane. In order to generate the amine groups on the surface for urease immobilization, NH3 plasma was used with RF power of 100 W for various times. The pH sensitivities of ITO/PET electrodes treated without and with NH3 plasma for 3 and 6 min were all around 51±4 mV/pH. However, the pH sensitivities of the samples treated with NH3 plasma for 9 min were slightly reduce to 45±5 mV/pH. In addition, the urea sensitivities of ITO/PET EGFET can be increased from 20.7 to 43.3 mV/pCurea by NH3 plasma from 3 to 9 min.