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Mapping electrical properties in working nanodevices

Study of nanocapacitors in working conditions by operando electron holography

par Guy Molénat - publié le , mis à jour le

The electrical potential distribution in metal-insulator-metal nanocapacitors under working conditions has been investigated using new methodology that combines advanced sample preparation, state-of-the-art electron holography and finite element modelling. Our results demonstrate that electrical properties such as electric field, capacitance and surface charge density of nanodevices directly extracted from production lines can be preserved and studied at the nanoscale.

Nano-electronic devices play an essential role in many domains, and their development and improvement attracts considerable attention in fundamental and applied research. In collaboration with STMicroelectronics (Crolles, France) and in the framework of the ANR project IODA, we have shown how electric fields in real nanodevices can be studied under working conditions using operando electron holography.

A specific sample preparation method was first developed to bias electron-transparent nanodevices extracted from production lines whilst ensuring their electrical connectivity and functionality without employing dedicated probe-based holders.

Using this approach based on focused ion beam (FIB) circuit modification, an array of parallel Metal-insulator-metal (MIM) nanocapacitors extracted from a matrix structure integrated in a STMicroelectronics 28 nm process test chip were prepared for transmission electron microscopy experiments.

Operando electron holography observations performed on the I2TEM microscope allowed the electric potential to be quantitatively mapped in the active areas, and between devices, whilst biasing the devices in situ

Left : Amplitude image of both MIM nanocapacitors in parallel and experimental phase image with isopotential contours of the induced electrostatic potential for 0.6V bias applied by the power supply. Right : Phase profiles extracted for different biases. Ta2O5 active layer is between the two TiN electrodes.

 

Experimental results were compared with finite element method (FEM) modelling simulations to determine local electrical parameters. We demonstrate that electrical properties such as capacitance and surface charge density can be quantitatively mapped at the nanoscale and have been preserved by our sample preparation methodology when compared to macroscopic measurements.

This work paves the way for mapping the local electrical properties of more complex biased devices such as MOS transistors or spintronic devices by adapting the sample preparation workflow to achieve a successful circuit modification and enable electrical stimulation of the device.This ability to study local electric fields quantitatively in newly proposed devices and devices already in production will help efforts to explore fundamental physical processes as well as to develop and improve current devices.

 

Publication :

This work was featured on the cover of the APL journal in which it was published.
Appl. Phys. Lett. 120, 233501 (2022) ; https://doi.org/10.1063/5.0092019

 

Contact : Christophe Gatel, christophe.gatel[at]cemes.fr