Electron trapping in HfO2-based MOS structures was studied through pulsed capacitance-voltage (C-V) technique. 10 nm HfO2 layer was deposited by atomic layer deposition over a HF last treated Si substrate. The C-V curves were observed to shift to positive voltages driven by the positive applied voltage along the pulses, consistent with electron trapping due to tunneling transitions between the substrate and pre-existing defects within the oxide and the subsequent lattice relaxation through electron-phonon interaction. The dependences of the voltage shift for a given capacitance value (Delta VC) with stress bias and time, allowed to distinguish two mechanisms. An initial trapping process occurs for times shorter than the microsecond, probably associated with a thin non-stoichiometric SiOx interfacial layer, which is followed by a trapping process that starts after tens of mu s and progressively slowed down, associated with traps within the HfO2 layer. Numerical simulations yield for the HfO2 traps an energy of 1.3 eV below the conduction band edge, decreasing exponentially with the distance from the Si interface with a characteristic length of 1.7 nm; and phonon and relaxation energies of 50 meV and 1 eV, respectively. These physical parameters are consistent with previous reports of electron trapping in HfO2 layers deposited on a controlled interfacial layer, suggesting that trapping properties of defects inside the HfO2 layer are insensitive to the treatment of the Si surface before HfO2 deposition. On the other hand, the observed large initial trapping suggests that the non-controlled SiOx interfacial region is more defective than a controlled one.

The response of n-channel field-oxide field-effect transistors (FOXFETs) exposed to ionizing radiation and annealing is reproduced using a physics-based numerical model that includes the microscopic processes leading to hole capture/ neutralization and generation of interface traps. The results show that a distribution for the proton emission rate has to be considered to reproduce the threshold voltage evolution with dose, and density of interface traps trends at both short and long post-irradiation annealing times if direct release is considered as the mechanism responsible for proton production. This result may suggest a failure of the usual simple drift-diffusion model for proton transport across SiO2 in total dose models, or a limitation of our model based on some processes that were neglected in the first approach, such as hydrogen cracking as a secondary mechanism for proton production.

The response of commercial-off-the-shelf CD4007 p-channel MOSFET exposed to 60Co radiation under switched-bias conditions is studied by real time monitoring the threshold voltage evolution with accumulated dose. The possibility to employ switched-bias techniques to recover threshold voltage is demonstrated. As reported for other devices, non-monotonic responses are observed. A physics-based numerical model that takes into account both charge buildup within the oxide and generation of interface traps is employed to reproduce the experimental results. The implications for dosimetry are discussed.

A physics-based numerical model is proposed as a simulation tool to predict the total ionizing dose response of CMOS integrated circuits. The model includes the radiation-induced charge buildup within both the gate oxide of the standard transistors and the bird's beak parasitic transistor due to LOCOS isolation method. The zero bias radiation response of standard MOSFETs is simulated, showing the difference between n- and p-channel transistors. For high dose levels, the charge buildup in the parasitic transistor leads to an increase of the off-state leakage current for nMOSFET. The radiation response of an inverter is shown as an example of the consequence this increment of the leakage current may cause to the simple CMOS circuit. The model showed to successfully predict the increment in the delay and the failure of the circuit for high absorbed doses.

The response of floating gate (FG) devices to 60 Co $\gamma $ -rays under switched bias conditions is studied by real-time monitoring of the threshold voltage evolution with accumulated dose. Samples were fabricated in a 1.5- $\mu \text{m}$ CMOS process, suitable for dosimetry applications. A physics-based numerical model of total ionizing dose (TID) effects in FG MOS devices is developed, taking into consideration the dominant microscopic processes leading to charge accumulation/neutralization across the structure. The main parameters of the model are the capture and neutralization rates in both oxides (tunnel and interpoly), and the initial FG charge. A dataset of experimental measurements is used to extract those parameters. Then, the model is applied to predict the response of later experiments. In one case, the device is irradiated under different switching bias voltages, yielding a mean absolute error of 1.8%. With the same set of parameters, but using another device, the model is able to predict with an error of 2.1%, an exposition performed with a $V_{t}$ -shift range twice the one in the first experiment. The predictive power of the model in a wide range of experimental conditions relies on the physics principles behind it. Combined experiments plus simulations allow to distinguish how charges in each layer of the structure evolve and contribute to the overall response. As an application of the model, cycled measurement technique for dosimetry is investigated.

Radiation-induced charge neutralization at different bias is studied for 230 nm p-channel MOS dosimeters under gamma-radiation. A physics-based numerical model is employed to reproduce the experimental results. Good agreement is obtained between measurements and simulations considering capture and neutralization rates independent of electric field during neutralization stages. Sensitivity curves during neutralization stages show a two part process consisting of a slow decrease for short times followed by a rapid fall. Remarkably, the model predicts this behavior and allows to understand that in terms of the potential well generated due to trapped holes within the oxide.

Interface degradation-induced shifts of MOSFET thermal coefficients and zero temperature coefficient current (IZTC) were studied by monitoring the interface traps (Nit) growth in a thick oxide n-channel MOSFET due to exposure to ionizing radiation, and to further annealing at room temperature. A new physics-based compact model was proposed to account for the observed results, and to predict the evolution of these parameters as interface traps are generated during stress. Within a range (0–40∘C) around room temperature, both the inverse of the mobility and the threshold voltage thermal coefficient varied roughly linear with Nit, with relative variations of 5.2×10−13eVcm2 and −9.33×10−13eVcm2, respectively. Furthermore, the dependence for IZTC with Nit can also be approximated to a linear expression, with a relative increment of 1.94×10−12eVcm2. The implications for temperature error mitigation in MOS sensors were discussed.

The response of MOS dosimeters fabricated using field oxide as gate insulator was characterized measuring the threshold voltage shift with absorbed dose. Sensitivity for different applied bias and threshold voltage evolution with dose for constant bias were experimentally obtained. A physics-based numerical model was developed to reproduce these measurements. The model includes the main physical processes leading to hole trapping and neutralization with the capture rate per free hole as the only fitting parameter. The model predicted further experiments of the zero bias sensitivity for an extended dose range. For low threshold voltage values, charge neutralization was observed. Simulations were insensitive to the value of the neutralization-related physical parameter, even during threshold voltage recovery. We showed that this result is related with the presence of a potential well for electrons within the oxide which drives the neutralization process. This dosimeter was compared to other thick oxide ones and different dosimetry considerations were discussed.

This paper presents the characterization of a thick gate oxide MOSFET for radiotherapy in-vivo dosimetry. The device is an N-channel transistor fabricated in a standard CMOS process using the Field Oxide as gate insulator. Sensitivity, fading, gate bias voltage dependence, percentage depth dose and angular response were assessed using a 6 MV LINAC. Experimental results showed that it is possible to estimate dose with a 3% uncertainty in a range up to 85 Gy with an average sensitivity of 62 mV/Gy. The measurement system noise equivalent dose is 3 mGy.

A new design for an on-chip ionizing radiation sensor is presented. The circuit consists of two source-coupled Field Oxide Transistors biased with the same drain current through a feedback loop, whose offset in the gate voltage is amplified. This paper explains the design criteria for integration of the sensor in a 0.5 μm CMOS process. The design was validated with simulations and showed the expected behavior.

We propose the use of a CMOS differential circuit with inherent amplification to enhance the performance of n-channel field oxide MOSFETs as ionizing radiation dosimeters. These new dosimeters are aimed to be used in low dose applications such as X-ray diagnosis. The circuit is presented and described, and a discrete-level prototype was tested as regards sensitivity, temperature variations compensation and signal-to-noise ratio at different operation conditions. Results show that, comparing to a single MOSFET dosimeter, on chip amplification is possible along with temperature induced error attenuation. The highest sensitivity measured with respect to gamma radiation was 0.4 V/rad. The circuit successfully measured the dose delivered in an X-ray image diagnosis environment with a sensitivity of approximately 0.5 V/rad.

We present in this paper a new circuit embedded sensor for ionizing radiation based on MOSFET dosimeters. The circuit presents differential sensing and inherent amplification, making it much more sensitive than standard MOS dosimeters. An n-channel Field Oxide transistor pair is used as the sensitive module of the circuit. The circuit was tested against γ-radiation and showed a non-linear responsivity and a maximum 58× amplification, corresponding to a sensitivity of 25.6 V/Gy. Then the circuit was tested against X-Ray beams and the response was corrected using the previous characterization, showing to be linear with the beam charge and dependent with the energy of the beam. These results indicate that the proposed circuit is suitable for X-Ray dosimetry.

This paper presents a new technique to build MOS dosimeters using unmodified standard CMOS processes. The devices are n-channel MOS transistors built with the regular Field Oxide as a thick radiation-sensitive gate. The devices were fabricated in two different commercial 0.6 μm CMOS processes, gate oxide thicknesses of ~600 nm and ~400 nm. Responsivities up to 4.4 mV/rad with positive bias, and 1.7 mV/rad with zero gate bias were obtained in the thicker oxides. The effect of charge trapped in the oxide and interface states on the shift in the threshold voltage are analyzed.

The evolution of the threshold voltage of MOS dosimeters during irradiation under switched bias is investigated with the aim of using the sensors with a new biasing technique. The devices response to a bias change does not only depend on the instant threshold voltage and bias, and may lead to non-monotonical behavior under fixed bias following the switch. This work shows experimental evidence for this effect and presents a simple model based on oxide charge buildup and neutralization. The proposed model reproduces the experimental data assuming the existence of two types of hole traps in the oxide. Physical interpretations of the results are discussed.

This work presents a differential MOS circuit for ionizing radiation dose estimation. Thick gate oxide n-MOS transistors are used as the sensing pair, with p-MOS load to enhance the radiation response. The circuit is analyzed and tested under gamma (60Co) radiation. Results show a radiation sensitivity increase up to 8 V/Gy and an improved thermal drift rejection ratio in comparison with a single n-MOS dosimeter.

MIS capacitance structures, with Hafnium Oxide, Alumina and nanolaminate as dielectrics were studied under gamma photons $^{60}{\hbox{Co}}$, 25 MeV oxygen ions and 10 MeV protons radiation using capacitance-voltage (C-V) characterization.

Through the injection of a Fowler-Nordheim tunnel current or the inversion of oxide fields during irradiation (Radiation-Induced Charge Neutralization), the oxide charge trapped in thick-oxide (300 nm) commercial RADFETs, often called Q(OT) could be erased. Novel trapped-hole and interface characteristics were observed after treatments of this type at high doses. With both erasure techniques, it was possible only to neutralize a fraction of the oxide trapped charge. A non negligible amount of charge and border traps is deemed here to be "intractable". That adjective an a symbol, Q(IN), are introduced for the first time in this paper. Later sections discuss the possible impact of these results. The conclusion for dosimetry is that a "reusable RADFET" dosimeter, working up to an unprecedented dose before wearing out, may be a practical possibility.

The charge trapping/detrapping under normal operating conditions in MOS devices with HfO 2 as insulating layer is studied. The hysteresis in the capacitance-voltage curves was analyzed and the voltage for a given capacitance was tracked in time. A simple tunneling front model is proposed in order to reproduce the observed curves and to obtain the relevant physical parameters.

MIS capacitive structures were studied under gamma, 16O and p radiation. The effects observed were registered employing C-V curves. Those showed different characteristics depending on the type of radiation and dielectric.