Growth of binary oxides on Si substrates: solid solutions of SiO2-GeO2 and HfO2-ZrO2

Functional oxides are materials with interesting properties for electronic applications. In this thesis, we investigate the growth of thin films of two types of oxides: mixtures of silicon oxide and germanium oxide, and mixtures of hafnium oxide and zirconium oxide. These mixtures can have varying amounts of their components, which we can use to change their properties.

Silicon and germanium oxide can adopt the alpha-quartz structure, which is piezoelectric (that is, they can convert electrical stimuli to a mechanical response, and vice versa). This is an important property for communications components. To make devices that operate at higher frequencies (5G and beyond), we would like to make ever smaller quartz elements. To do this, we grow silicon and germanium oxide thin films in a non-crystalline, thus non-piezoelectric state. We can do this by alternating layers of pure silicon oxide with layers of pure germanium oxide using a chemistry-based method (Atomic Layer Deposition), or by growing a mix of the two using a physics-based method (Pulsed Laser Deposition). Then, we guide them into the correct crystalline form in a high temperature furnace.

Hafnium and zirconium oxide are peculiar in that they can be ferroelectric (which has applications in memory storage) but only when they are grown in very thin films. We investigate their behavior when these films are grown by Pulsed Laser Deposition on silicon substrates (the most common substrate type in industry). In both cases, we investigate the results using various techniques, mainly based on X-ray diffraction and electron microscopy.