System and method of measuring high-speed electrical waveforms using force microscopy and offset sampling frequencies
First Claim
1. An apparatus for measuring a periodic electrical waveform existing proximate the surface of a sample, said periodic waveform having a predefined repetition frequency, comprising:
- a sampling signal generator that generates a sampling signal having a sample signal repetition frequency offset from said predefined repetition frequency by a difference frequency;
a cantilever coupled to said sampling signal generator for carrying said sampling signal to a position proximate the surface of said sample so as to generate an electrical force on said cantilever that is a nonlinear function of differences in amplitude between said sampling signal and said periodic electrical waveform, said electrical force displacing said cantilever such that said cantilever'"'"'s displacement replicates said electrical waveform at a repetition rate equal to said difference frequency;
wherein said cantilever has a mechanical resonance frequency that limits said cantilever'"'"'s speed of movement, said mechanical resonance frequency is substantially less than said predefined repetition frequency, and said sample signal repetition frequency is set such that said difference frequency is less than said mechanical resonance frequency;
whereby said cantilever low pass filters, with a cutoff frequency corresponding to said mechanical resonance frequency, said electrical force on said cantilever; and
a displacement sensor for detecting said displacement of said cantilever.
3 Assignments
0 Petitions
Accused Products
Abstract
A potentiometry apparatus for measuring a periodic electrical waveform existing proximate the surface of a sample such as a semiconductor wafer is disclosed herein. The potentiometry apparatus includes a pulse generator for generating a sequence of electrical pulses at a pulse frequency offset from the frequency of the surface waveform by a mixing frequency. A cantilever coupled to the pulse generator serves to carry the electrical pulses to a position proximate the surface of the sample. In a capacitive displacement mode the cantilever is mechanically displaced so as to generate a time-expanded representation of the electrical surface waveform having a repetition frequency equal to the mixing frequency. During displacement mode operation an optical detection circuit may be employed to monitor deflection of the cantilever. In a tunneling current mode the cantilever is again employed to carry the electrical pulses to a position proximate the surface of the sample. In this mode a tunneling current propagating through the cantilever at the mixing frequency provides a time-expanded representation of the electrical surface waveform.
-
Citations
20 Claims
-
1. An apparatus for measuring a periodic electrical waveform existing proximate the surface of a sample, said periodic waveform having a predefined repetition frequency, comprising:
-
a sampling signal generator that generates a sampling signal having a sample signal repetition frequency offset from said predefined repetition frequency by a difference frequency; a cantilever coupled to said sampling signal generator for carrying said sampling signal to a position proximate the surface of said sample so as to generate an electrical force on said cantilever that is a nonlinear function of differences in amplitude between said sampling signal and said periodic electrical waveform, said electrical force displacing said cantilever such that said cantilever'"'"'s displacement replicates said electrical waveform at a repetition rate equal to said difference frequency; wherein said cantilever has a mechanical resonance frequency that limits said cantilever'"'"'s speed of movement, said mechanical resonance frequency is substantially less than said predefined repetition frequency, and said sample signal repetition frequency is set such that said difference frequency is less than said mechanical resonance frequency;
whereby said cantilever low pass filters, with a cutoff frequency corresponding to said mechanical resonance frequency, said electrical force on said cantilever; anda displacement sensor for detecting said displacement of said cantilever. - View Dependent Claims (2, 3, 4)
-
-
5. A method for measuring a periodic electrical waveform existing proximate the surface of a sample, said periodic waveform having a predefined repetition frequency, comprising the steps of:
-
generating a sampling signal having a sample signal repetition frequency offset from said predefined repetition frequency by a difference frequency; transmitting said sampling signal along a signal path integrated with a cantilever to a position proximate the surface of said sample so as to generate an electrical force on said cantilever that is a nonlinear function of differences in amplitude between said sampling signal and said periodic electrical waveform, said electrical force displacing said cantilever such that said cantilever'"'"'s displacement replicates said electrical waveform at a repetition rate equal to said difference frequency; wherein said cantilever has a mechanical resonance frequency that limits said cantilever'"'"'s speed of movement, said mechanical resonance frequency is substantially less than said predefined repetition frequency, and said sample signal repetition frequency is set such that said difference frequency is less than said mechanical resonance frequency;
whereby said cantilever low pass filters, with a cutoff frequency corresponding to said mechanical resonance frequency, said electrical force on said cantilever; anddetecting said displacement of said cantilever. - View Dependent Claims (6, 7, 14)
-
-
8. An apparatus for measuring a periodic electrical waveform existing proximate the surface of a sample, said periodic waveform having a predefined repetition frequency, comprising:
-
a sampling signal generator that generates a sampling signal having a sample signal repetition frequency that is offset from said predefined repetition frequency by a difference frequency; a mechanical sensor coupled to said sampling signal generator for carrying said sampling signal to a position proximate the surface of said sample so as to generate an electrical force on the mechanical sensor that is a nonlinear function of differences in amplitude between said sampling signal and said periodic electrical waveform, said electrical force displacing said mechanical sensor such that said sensor'"'"'s displacement replicates said electrical waveform at a repetition rate equal to said difference frequency; wherein said mechanical sensor has a mechanical resonance frequency that limits said mechanical sensor'"'"'s speed of movement, said mechanical resonance frequency is substantially less than said predefined repetition frequency, and said sample signal repetition frequency is set such that said difference frequency is less than said mechanical resonance frequency;
whereby said mechanical sensor low pass filters, with a cutoff frequency corresponding to said mechanical resonance frequency, said electrical force on said mechanical sensor; anda displacement sensor for detecting said displacement of said mechanical sensor. - View Dependent Claims (9, 10, 11, 12, 13)
-
-
15. A method for measuring a periodic electrical waveform existing proximate the surface of a sample, said periodic waveform having a predefined repetition frequency, comprising the steps of:
-
generating a sampling signal having a sample signal repetition frequency offset from said predefined repetition frequency by a difference frequency; transmitting said sampling signal along a signal path integrated with a mechanical sensor to a position proximate the surface of said sample so as to generate an electrical force on said mechanical sensor that is a nonlinear function of differences in amplitude between said sampling signal and said periodic electrical waveform, said electrical force displacing said mechanical sensor such that said mechanical sensor'"'"'s displacement replicates said electrical waveform at a repetition rate equal to said difference frequency; wherein said mechanical sensor has a mechanical resonance frequency that limits said mechanical sensor'"'"'s speed of movement, said mechanical resonance frequency is substantially less than said predefined repetition frequency, and said sample signal repetition frequency is set such that said difference frequency is less than said mechanical resonance frequency;
whereby said mechanical sensor low pass filters, with a cutoff frequency corresponding to said mechanical resonance frequency, said electrical force on said mechanical sensor; anddetecting said displacement of said mechanical sensor. - View Dependent Claims (16, 17, 18, 19, 20)
-
Specification