Improved FIB-Based Fabrication of an Operative Pt/HfO₂/TiN Device for Biasing and/or Heating TEM Using an In Situ FIB Method

In situ biasing Transmission Electron Microscopy (TEM) is a powerful technique to reveal morphological and structural changes in non-volatile memories such as HfO₂ based Resistive Random Access Memory (RRAM) devices at the nanoscale during set and reset operations. One of the main limitations in the application of in situ biasing TEM is the Focused Ion Beam (FIB)-based lamella sample preparation. Apart from the complicated and tedious sample preparation process, it also yields a relatively low success rate and, as a result, makes it very time consuming for researchers.<br/>In general, preparing a clean and electrically connected sample for biasing without an electrical short circuit is a challenging task. There are a lot of pitfalls when preparing FIB lamellas for electrical experiments. Often, the preparation process has to be repeated several times before obtaining successfully contacted and fully functional sample. These repetitions require additional costly FIB and TEM time.<br/>In this contribution, we present a new approach of preparing and characterizing TEM lamella of HfO₂-based RRAM devices prior to in situ experiments in the TEM with increased reliability. This method is based on the use of a novel Microelectromechanical Systems (MEMS) Nano-Chip especially designed for simultaneous biasing and heating experiments in the TEM. The method relies on the use of a modified Scanning Electron Microscope (SEM) stub that allows to apply in situ stimuli during sample preparation, e.g. in situ FIB stub. The stub has electrical connections to drive electrical signals to the sample and is specifically designed to prepare the FIB lamella on the MEMS chip in one go (without breaking the vacuum). During the whole preparation process, the sample can be biased to check for short circuits and for proper electrical connection, ensuring current flow through the lamella. We will also discuss how the method can be employed to do further characterization of the sample inside an FIB/SEM dual beam system and how it correlates with the in situ biasing TEM results.