Controlling the TiN Electrode Work Function at the Atomistic Level: A First Principles Investigation

Arrigo Calzolari,Alessandra Catellani

doi:10.1109/access.2020.3017726

Abstract

The paper reports on a theoretical description of work function of TiN, which is one of the most used materials for the realization of electrodes and gates in CMOS devices. Indeed, although the work function is a fundamental quantity in quantum mechanics and also in device physics, as it allows the understanding of band alignment at heterostructures and gap states formation at the metal/semiconductor interface, the role of defects and contaminants is rarely taken into account. Here, by using first principles simulations, we present an extensive study of the work function dependence on nitrogen vacancies and surface oxidation for different TiN surface orientations. The results complement and explain a number of existent experimental data, and provide a useful tool to tailoring transport properties of TiN electrodes in device simulations.

Highlights

The metal-insulator-metal (MIM) integrated capacitors are key device structures for modern analog and radio frequency integrated circuits [1]
It is generally assumed that TiN has a work function (WF)≈ 4.7 eV, even though this value can be modulated over a large energy range 4.1-5.3 eV, depending on the growth characteristic of the sample, the coupling with semiconductor or metal-oxide substrates or temperature treatments [10]–[13]
TiN undergoes surface oxidation [24], [25]: this happens both when as-grown films or fresh cleavage surfaces are exposed to air [26], [27], and when TiN is in contact with other metal oxides

Summary

INTRODUCTION

The metal-insulator-metal (MIM) integrated capacitors are key device structures for modern analog and radio frequency integrated circuits [1] This includes both two-terminal devices such as in ovonic selectors [2], [3], and layered gates in connection with high-κ metal-oxide dielectrics, such as, HfO2 [4], TiO2 [5], SiO2 [6], [7], and Al2O3 [8]. TiN(111) surface is modeled via a non-polar off-stoichiometric slab with Titermination on both external faces (Figure 1c), in agreement with previous theoretical simulations [14]. Defective TiNx systems are simulated including an increasing number of N vacancies (VN ) in the reference slabs

RESULTS AND DISCUSSION

SURFACE OXIDATION

CONCLUSION