Recently developed scanning nonlinear dielectric microscopy for measuring semiconductor and ferroelectric materials

21.12.2021 13:00 – 14:30

In this seminar, recently developed scanning nonlinear dielectric microscopy (SNDM) for measuring semiconductor and ferroelectric materials is introduced.
At first, time resolved scanning nonlinear dielectric microscopy (tr-SNDM) is introduced. The conventional imaging mode of SNDM can resolve local voltage-dependent differential capacitance (dC/dV) reflecting local carrier density, interface defects, and fixed charges in semiconductor materials and spontaneous polarizations in ferroelectrics.
In order to give the further nanoscale details of the materials, here a new method for the simultaneous local capacitance-voltage (CV), dC/dV-V, and DLTS measurements by using recently developed tr-SNDM is introduced.
By utilizing modern high speed digital facilities, tr-SNDM realizes wider measurement bandwidth and more highly flexible post-processing than the conventional SNDM using traditional analog electronics such as a frequency demodulator and lock-in amplifier. Tr-SNDM can directly record the time series of the sensor output by a high-speed digitizer and demodulate the capacitance response to an arbitrary applied voltage at each measurement point by offline post-processing. So far, tr-SNDM enable us to perform simultaneous local CV, dC/dV-V, and DLTS measurements. This new method is applied to investigate semiconductor MOS interface.
Next, nanoscale ferroelectric domain dynamics characterization using Local C-V mapping is introduced. Nanoscale characterization of polarization switching behavior is important in the future development of piezoelectric and ferroelectric devices. Recently, we have developed a novel probe microscopy technique for local C-V mapping based on SNDM. This method enables detailed analysis of dynamic polarization switching behavior beyond the conventional static domain observation.
An SNDM system has an LC oscillator probe, which enables local capacitance deviation to be detected with high sensitivity. In a conventional SNDM observation, an AC bias voltage below a domain switching voltage is applied to a sample, and a nonlinear response is detected to visualize the static domain structure. On the other hand, in the novel method, the response is measured with a large-amplitude AC bias above the polarization switching voltage. For ferroelectric films, C-V curves observed in this way draw a butterfly curve, as with macroscopic measurements. By analyzing such local C-V butterfly curves, various parameters related to polarization switching can be obtained.
In this talk, two application examples are introduced. The first example is the characterization of a bulk single-crystal LiTaO3. In this example, we revealed that anomalous C-V curves were observed in the vicinity of domain boundaries. Such C–V curves are considered to reflect domain wall movement due to the electric field. The second example is the characterization of a HfO2-based ferroelectric thin film. Since the prepared film had random grain orientations, the shape of the observed C-V curves varied depending on the position. Parameter extraction from the obtained dataset enabled to visualize the in-plane distributions concerning the net switchable polarization amount, the intrinsic coercive field, and the local imprint.

Lieu

Bâtiment: Ecole de Physique

Auditoire Stuckelberg

Organisé par

Faculté des sciences
Département de physique de la matière quantique

Intervenant-e-s

Yasuo CHO, Professor - Research Institute of Electrical Communication Tohoku University, Japan

entrée libre

Classement

Catégorie: Séminaire