Streamlined In-Situ MEMS-Chip Fabrication for Electrical and Electro-Thermal (S)TEM Studies via Optimized FIB Methodology

Transmission electron microscopy (TEM) with in-situ electrical and electro-thermal probing demands pristine, contamination-free electron-transparent samples. Focused ion beam (FIB) milling used for site-specific TEM sample preparation often introduces artifacts that hinder accurate electrical measurements. Here, we present a novel and optimized FIB-based methodology specifically designed for in-situ studies on micro-electro-mechanical-system (MEMS) chips.<br/>Our approach [1, 2] minimizes manipulation steps and Pt deposition, one of the main sources of contamination. Crucially, we introduce an alternative lamellae orientation during the lift-out procedure that enables direct attachment onto the MEMS chip, eliminating the need for a separate attachment/detachment steps and, hence, minimizing potential contamination. This methodology is universally applicable for depositing lamellae on any MEMS chip or flat surface.<br/>We systematically investigated the impact of key sample preparation parameters on the electrical performance of the final lamellae. First, we examined the influence of Pt contact size and position. Samples featuring Pt contacts deposited across the top surface exhibited superior stability and reproducibility compared to those with limited sidewall contacts. This suggests a more robust electrical connection due to increased contact area. Second, we explored the effect of incident Ga beam energies (30 kV vs. 8 kV) during Pt contact deposition. Lamellae prepared with a 30 kV Ga beam displayed cleaner surfaces and sharper contact edges. Furthermore, these differences in surface morphology translated to distinct measured electrical responses, highlighting the critical role of minimizing contamination for accurate electrical characterization. Finally, we investigated the effect of different lamellae thicknesses and the incorporation of specific slit geometries on the electrical measurements. High-resolution STEM imaging and spectroscopy confirm the excellent quality of the prepared samples.<br/>This optimized FIB methodology, based on a novel geometry and streamlined processing, represents a significant advancement for in-situ TEM studies of electrical and electro-thermal phenomena in diverse materials amenable to standard FIB preparation.<br/><br/>References:<br/>[1] Srot V <i>et al.</i>, Microscopy and Microanalysis 29 (2023) 596-605. doi.org/10.1093/micmic/ozad004<br/>[2] Protochips Webinar Series Sample Preparation in In Situ TEM, Part 3 https://www.youtube.com/watch?v=ZjnSc6NPmEA