Ultra-thin platinum : nucleation to application

The ability to deposit thin, conformal films is very important given the down-scaling of devices. Pt, in particular, has attracted considerable attention for thin film applications in micro and nano-electronic devices due to its chemical inertness, high work function, and excellent electrical properties, including a linear temperature coefficient of resistance (TCR), over a wide temperature range. However, the use of Pt in devices has been somewhat limited, both because of material cost and limitations caused by the directionality of conventional Pt deposition techniques. In this work, thin Pt films as thin as 3.7 nm were deposited using Plasma Enhanced Atomic Layer Deposition (PEALD), and electrical properties of thin Pt films were measured. In addition, some potential application areas for thin Pt films were explored. Chapters 3 and 4 of this dissertation discuss lowering the thickness limit of current Pt films, and how these films' electrical properties change according to thickness. Here in this work, by changing the nucleation layer to TiO2 from Al2O3, the non-ideal nucleation behavior of Pt was mitigated. With this change, the previous thickness limit of electrical continuous Pt, reported to be 8 nm, was pushed to 4 nm. The electrical properties of these thin Pt films, electrical conductivity and Temperature Coefficient of Resistance (TCR), were measured. While Pt films down to 5.7 nm followed the theoretical models very well, Pt films thinner than 5.7 nm deviated from the theory due to incomplete coverage. Nonetheless, Pt film with a thickness of 3.7 nm was deposited on TiO2 and showed good electrical conductivity and electrical stability; the results show that Pt films could be used for Resistance Temperature Detectors (RTDs) for next-generation micro/nano-electromechanical devices. Two potential application areas of thin Pt are discussed in the last two chapters of this dissertation: wearable and flow sensing applications. In chapter 5, thin Pt films' ability to be used as a flexible electrode was studied for wearable application. Pt deposited on flexible substrates had a similar electrical property and TCR as Pt deposited on rigid substrates, and also demonstrated remarkable stability during a bending test, showing within 1% drift in electrical conductivity after 1000 cyclic bending tests. In chapter 6, fabrication and testing of the first thinnest PEALD Pt anemometer is discussed. In addition, with U-Trench technique, novel corrugated beam design and its effect on anemometer performance is discussed. For 20 nm thick Pt sensing element, wind velocities between 1.5 - 18 m/s could be sensed by using as little as 3 mW with the response time of 3.74 ms. Moreover, when the sensing element was wide as 20 um, adding corrugation to the sensing element heated the sensing element more than the sensing element with no corrugation, thereby increasing the anemometer performance significantly. In summary, Pt showed remarkable performances for both applications, proving its potential importance for next-generation micro/nano-electromechanical devices.

Keywords: Mechanical Engineering.
Advisor: Kenny Thomas William 
Goodson Kenneth E.
Prinz F. B.