Acoustic Scanning Probe Microscopy with Composite Pulse Excitation
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Solution Overview
Problem
Acoustic scanning probe microscopy systems face challenges in detecting small embedded structures beneath a substrate surface due to the formation of standing waves caused by continuous wave acoustic input signals, which degrade the signal-to-noise ratio.
Innovation Solution
The method involves applying a composite acoustic input signal composed of multiple frequency components, which together mimic a pulse signal of limited duration, thereby preventing the formation of standing waves and improving signal quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of stationary object
If a continuous wave acoustic input signal is applied to the substrate, then the acoustic signal can be continuously transmitted through the substrate material, but standing waves are formed due to scattering at boundaries and interfaces, degrading the signal-to-noise ratio
Solution Approach 1:
The patent applies periodic pulsed acoustic excitation instead of continuous wave excitation. The acoustic signal is transmitted in discrete pulses separated by silent periods, which prevents the formation of standing waves while maintaining continuous capability through repeated pulsing. This resolves the contradiction by using periodic action to eliminate harmful standing waves while preserving continuous measurement capability.
2Measurement precision
If a very short pulse signal (less than a microsecond) is applied to prevent standing waves, then the signal-to-noise ratio improves, but the system cannot accommodate such short pulse durations due to continuous wave excitation limitations
Solution Approach 1:
The patent makes the excitation signal dynamic and adjustable, transitioning from fixed continuous wave excitation to variable pulsed excitation. The system can adaptively control pulse duration, amplitude, and repetition rate based on measurement requirements. This dynamic capability allows the system to achieve very short effective pulse durations (less than a microsecond) while maintaining flexibility in operation, resolving the contradiction between signal quality and system capability.
3Measurement precision
If acoustic energy is applied to detect embedded structures, then subsurface features can be visualized, but the acoustic signal is scattered by any encountered boundary or structure including outer surfaces and internal layers, creating noise
Solution Approach 1:
By using pulsed excitation with silent periods between pulses, the system allows the acoustic field to fully decay and eliminates overlapping reflections from different depths. This periodic action separates the detection of different subsurface features in time, reducing scattering noise from multiple boundaries while maintaining detection capability for embedded structures.
Solution Approach 2:
The patent employs frequency modulation to rapidly sweep through a broad frequency range during each pulse cycle, effectively 'rushing through' the frequency spectrum. This allows the system to skip over problematic frequency ranges that cause standing waves and focus energy on frequency bands that penetrate deeper into the substrate, reducing noise from superficial structures while detecting deeper embedded features.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enables high-resolution visualization of small embedded features by enhancing the signal-to-noise ratio and reducing noise interference, thus overcoming the limitations of continuous wave signals.
Implementation Method 1
the acoustic input signal has a frequency above 1 gigahertz; detecting, using a probe of a scanning probe microscope, an acoustic return signal from the substrate... the acoustic input signal is conveyed by the substrate material and will be scattered by structures embedded within the substrate. At the surface of the substrate, this scattering will be visible in the return signal's phase and amplitude
Implementation Method 2
The mixing of the both frequencies provides a frequency component at the difference frequency, which can be sensed by the probe and provides the information about the subsurface geometry and embedded structures... the acoustic return signal is picked up by the probe being (continuously or at least for a small period) in contact with the surface
Implementation Method 3
use is typically made of downmixing of frequencies of a heterodyne signal. In accordance therewith, the acoustic input signal consists of at least two frequencies (e.g. a carrier frequency and a modulation frequency) in the gigahertz range, having a frequency difference at a much lower frequency (i.e. within a measurable frequency range of the probe)
Data Source
AI summary
The present document relates to a method of performing acoustic scanning probe microscopy for imaging structures underneath a substrate surface, comprising: applying an acoustic input signal to the substrate having a frequency above 1 gigahertz, detecting a return signal, and analyzing the return signal for obtaining information on the embedded structures. The step of applying the acoustic input signal comprises applying a plurality of acoustic signal components which each include a selected frequency. The step of detecting includes detecting a response signal for each of the plurality of acoustic signal components. The frequencies are selected such that the components provide a composite signal being a pulse signal of limited time duration. The invention is further directed at a scanning probe microscopy system and a computer program product.