Development of Ferroelectric Hafnium Oxide for Negative Capacitance Field Effect Transistors

Abstract: With the transistor being the workhorse in modern electronics it has been vastly improved since its invention. However, the previous go-to improvement method of scaling it down has reached a dead end. Power dissipation has become a large concern and is in need of a solution. In the pursuit of further improving the transistor structure and its performance new approaches are being evaluated. A very promising approach is the integration of ferroelectric materials enabling negative capacitance. With subthreshold slopes below 60 mV/decade demonstrated and hence enabling lower operation voltage a new era of transistor technology is protruding. In this thesis a new recipe for deposition of hafnium oxide thin films using plasma enhanced atomic layer deposition has been developed. Thin hafnium oxide films have been fabricated, characterized and their properties optimized. The films are embedded into a titanium nitride metal-insulator-metal (MIM) structure for electrical characterization. With the use of Poole-Frenkel, Schottky and Fowler-Nordheim models the leakage current mechanisms of the thin films have been evaluated. For the first time, observation of the ferroelectric characteristics in undoped hafnium oxide thin films grown using plasma enhanced atomic layer deposition are reported. The presence of ferroelectricity was confirmed with polarization measurements, with values of the remanent polarization $P_r$ up to 8.75$\mu$C/cm$^2$ for a 10nm thick film with a dielectric constant $\epsilon_r$ up to 30.