In this study, we control the oxidant dose to promote ferroelectricity in dopant-free ALD hafnium oxide films. By lowering the oxidant dose during growth, we show that we can achieve near total suppression of the monoclinic phase in sub-10 nm hafnium oxide films with no major impurity doping. Using metal-insulator-metal structures, we demonstrate that lowering the oxidant dose can give rise to a six-fold improvement in remanent polarization. Using this technique, we observe a remanent polarization of 13.5 μC/cm2 in a 6.9 nm-thick hafnium oxide film and show that some ferroelectricity can persist in pure hafnium oxide films as thick as 13.9 nm. Using a trap-assisted tunneling model, we show the relationship between the oxidant dose and oxygen vacancy concentration in the films, suggesting a possible mechanism for the suppression of the monoclinic phase.

In this work, the ferroelectric properties of nanolaminates made of HfO and ZrO were studied as a function of the deposition temperature and the individual HfO/ZrO layer thickness before and after electrical field cycling. The ferroelectric response was found to depend on the structure of the nanolaminates before any postdeposition annealing treatment. After annealing with a TiN cap, an "antiferroelectric-like" response was obtained from nanolaminates deposited in an amorphous state at a lower temperature, whereas a ferroelectric response was obtained from nanolaminates deposited at a higher temperature, where crystallites were detected in thick films before annealing. As the individual layer thicknesses were decreased, an increased lattice distortion and a concurrent increase in remanent polarization were observed from the nanolaminates deposited at high temperatures. After field cycling, nanolaminates deposited at lower temperatures exhibited an antiferroelectric-like to ferroelectric transition, whereas those deposited at higher temperatures exhibited a larger remanent polarization. Finally, we demonstrate that by leveraging the proper choice of process conditions and layer thickness, remanent polarizations exceeding those of the HfZrO solid solution can be obtained.

The Field Effect sensors are broadly used for detecting various target analytes in chemical and biological solutions. We report the conditions under which the pH sensitivity of an Ion Sensitive Field Effect transistor (ISFET) sensor can be significantly enhanced. Our theory and simulations show that by using pH buffer solutions containing counter-ions that are beyond a specific size, the sensor shows significantly higher sensitivity which can exceed the Nernst limit. We validate the theory by measuring the pH response of an extended gate ISFET pH sensor. The consistency and reproducibility of the measurement results have been recorded in hysteresis free and stable operations. Different conditions have been tested to confirm the accuracy and validity of our experiment results such as using different solutions, various oxide dielectrics as the sensing layer and off-the-shelf versus IC fabricated transistors as the basis of the ISFET sensor.

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