JPH0232576A - Detection of faint signal - Google Patents

Abstract

PURPOSE:To accurately read a faint signal by displacing the faint signal changing from time to time on a display, observing the change in the signal, and processing and detecting the faint signal by instructions from an input unit. CONSTITUTION:Parameters required for measurement of hole mobility are inputted through an input unit of a drive device 11, and a CPU incorporates therein those parameters and successively plots measured data on a CRT of the device 11 for preparation of a graph. In the measurement of the hole mobility, a magnetic field is applied to a semiconductor thin film sample 13 with a current supplied from a current source 14 in response to the hole mobility. Hereby, a signal voltage responsible to the mobility is generated. The signal voltage is measured by a digital voltmeter 17 through buffer amplifiers 15, 16. The CPU 12 plots the measured voltage on the graph on the CPU, successively. An operator watches the graph and effects the measurement at a position where the signal is stabilized. The CPU 12 records the measurement data on a printer 18.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a small signal detection method used for Hall mobility measurement and the like.

[Conventional technology]

Evaluation of hole mobility is essential in evaluating the electrical properties of semiconductor thin films, and the hole mobility of semiconductor thin films is measured and evaluated based on the results.

[Problem to be solved by the invention]

When measuring the hole mobility of a semiconductor thin film, since the semiconductor thin film has a high resistance (more than 106 Ω cm), the measurement signal is very small (mV to μV), making it difficult to read the signal accurately. .

In view of these points, it is an object of the present invention to provide a minute signal detection method that can accurately read signals.

Means for Solving CC11A] In order to achieve the above object, the present invention displays minute signals that change moment by moment on a display device to produce changes in the minute signals, and then displays the minute signals based on instructions from an input device. Processing and Detecting Signals 9 [Example] In an example of the present invention, the hole mobility of a semiconductor thin film is measured by a measuring device, and the ever-changing minute measurement signal is displayed using a CRT (cathode ray tube). This is displayed on a device, and the operator turns on and off the magnetic field applied to the semiconductor thin film while actually viewing the minute measurement signals. After the measurement is completed, a line is drawn on the CRT signal at the point where the magnetic field changes from off to on, as shown in Figure 5, and a line is drawn on the measurement signal on the CRT to the point where the magnetic field changes from off to on. Determine the range to be expanded to the boundary, for example, the range consisting of 30 measurement data before and after the point where the magnetic field is turned on from off, and then
As shown in the figure, the measurement signal on the CRT is enlarged and displayed by that range. Next, the operator determines the slope of the straight line shown by the measurement data before and after the point where the magnetic field is turned on from off, as shown in Figure 7, which is the range where the measurement signal on the CRT is stable. By determining B and CD and instructing them with an input device, the slope of the measurement data in the ranges AB and CD is determined by the method of least squares and a signal is detected. In this case, the signal is obtained by taking the least squares of each measurement data between AB and CD and extrapolating it to the value when the magnetic field is on. As shown in Figure 8, this extrapolated value is a correct value compared to the signal obtained by finding the average values of the ranges A-B and C-D where the measurement data is stable and taking the difference. Become.

If this value is V, then the Hall mobility μ of sample 13 is μ=
d −R/p −B (R=V/I). Here, d is the film thickness of the sample 13, R is the Hall resistance of the sample 13 when a magnetic field is applied, ρ is the resistivity of the sample 13, B is the strength of the magnetic field, and I is the current value of the current source 14.

FIG. 1 shows the apparatus used in this embodiment, and FIG. 2 is a flowchart showing the program of the computer (CPU) 12 in this apparatus.

The drive device 11 includes an input device consisting of a display device using a CRT and a keyboard. The CPU 12 takes in the parameters necessary for measuring the Hall mobility inputted by the input device, and creates a graph on the CRT in order to sequentially plot the measurement data on the CRT. Next, hole mobility is measured. A magnetic field is applied to the semiconductor thin film sample 13 by a magnetic field generator, and a current I is supplied from a current source 14 to generate a signal voltage according to the hole mobility.

This signal voltage is measured by a digital voltmeter 17 via a buffer amplifier 15.16 having an input impedance of 101 sΩ, and the CPU 12 uses the digital voltmeter 17 in a measurement/data plotting routine Measurement-1.
7 measurement voltages are taken in and sequentially plotted on a graph on the CRT. In this embodiment, the operator can select a stable range of the measurement signal and use it for signal detection.
To make it easier for U12 to select this range, we will expand the area around where the magnetic field of the measurement signal on the CRT is turned on.
The CPU 12 sets the enlargement range, enlarges the measurement signal on the CRT by the range, and plots it. And C.P.
U12 calculates a signal based on the measurement signal on the CRT in a signal output calculation routine Ave.

Figure 3 shows the above measurement and data plotting routine.
Indicates rement-1. The CPU 12 sets the range on the CRT where the graph was created as the data plot range, and clears the digital voltmeter (Digipol) 17. Next, the CPU 12 sets the digital voltmeter 17 to a measurement state, waits for a certain number of seconds (here, an arbitrary number of seconds, 5 tep time), and then reads the data from the digital voltmeter 17 and plots it on a graph on the CRT. Thereafter, the CPU 12 repeats this operation, and the operator applies a magnetic field using the magnetic field generator at any time while holding the CRT. CP when a magnetic field is applied
U12 similarly reads data from the digital voltmeter 17 and plots it on a graph on the CRT, but when the magnetic field is turned on from off, it reads the time measured by the timer and the output voltage of the digital voltmeter 17, and Add a number. Then, when the measurement is completed, the CPU 12
A line is drawn and displayed at the point where the magnetic field in the measurement signal on T turns from off to on.

FIG. 4 shows the signal output calculation routine Ave.

When the magnetic field is turned on, the CPU 12 causes the printer 18 to print out the number. The operator refers to this number and uses the input device to input the number of stable data to be averaged before and after the magnetic field is turned on. The CPU 12 displays the data number on the display device, and when the operator re-inputs the data number, displays the re-input data number on the display device. Next, the CPU 12 calculates the average value of the data of that number before and after the magnetic field is turned on, and uses the method of least squares to find the slope of the straight line represented by the data before and after the magnetic field is turned on. Next, the CPU 12 calculates each average value and the difference between the data before and after the magnetic field is turned on, and causes the printer 18 to print them out.

Next, the CPU 12 plots on the CRT the time and voltage when the magnetic field was turned on from off, the average value and difference of each data before and after the magnetic field was turned on, and the above slope, and Draw a vertical line where the magnetic field turns on, and plot the straight lines before and after the magnetic field turns on, which were determined by the least squares method.

〔Effect of the invention〕

As described above, according to the present invention, a minute signal that changes every moment is displayed on a display device so that the change can be seen, and the minute signal is processed based on an instruction from an input device to detect the signal. It becomes possible to read the signal accurately.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an apparatus used in an embodiment of the present invention, FIG. 2 is a flowchart showing a CPU program in the same embodiment, and FIG. 3 is a flowchart showing a measurement/data plotting routine in the same program. Fourth
The figure is a flowchart showing the signal output calculation routine in the same program, Figure 5 is a diagram showing an example of Hall voltage detection by the above device, Figure 6 is an enlarged view of a part of the same Hall voltage detection example, and Figure 7 is and FIG. 8 are diagrams for explaining the above embodiment. 11... Drive device, 12... CPU. Ryoin Ryo ■ Time (3a)

Claims (1)

[Claims] A method for detecting a minute signal, characterized in that the minute signal that changes moment by moment is displayed on a display device so that the change can be seen, and the minute signal is processed and detected based on an instruction from an input device.