JPH0763795A - Electric field detector - Google Patents

Abstract

PURPOSE:To carry out calibration-free absolute voltage measurement by providing an electrode over the whole surface of a device whose optical characteristics change by electric fields and by controlling this electrode so as to reach the same potential as an electrode under measurement. CONSTITUTION:An optical beam 100 from a light source 5 passes through a polarizer 6, a wavelength plate 7, and a conductive transparent electrode 4, enters an electrooptical crystal 1, reflects on the bottom surface, passes again through the polarizer 6, enters a detector 8, and its output varies in accordance with the voltage between the electrode under measurement 3 and the electrode 4. A subtractor 10 calculates each output difference between the detector 8 and a reference signal generator 9, and a control circuit 11 impresses voltage on the electrode 4 according to this output. At this time, the voltage of the electrode 4 is controlled so that the output of the subtractor 10 may be zero. Equalizing the output of the generator 9 to the output of the detector 8 as the voltage between the electrode 3 and the electrode 4 is zero always enables the voltage between the electrodes 3, 4 to be zero, that is, reach the same potential. Therefore, when the impressed voltage of the electrode 4 is extracted as an output signal 200, its voltage equals the voltage of the electrode 3.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention is used for testing integrated circuits. In particular, the present invention relates to an electric field detection probe in which an electro-optical element is arranged close to an integrated circuit substrate and an electric field from an electrode of the integrated circuit optically measures a change in a physical state of the element.

[0002]

2. Description of the Related Art FIG. 9 is a diagram showing a configuration example of a conventional electric field detection probe and a measuring method thereof. At the time of measurement, the electro-optic crystal 1 is arranged close to the circuit board 2 to be measured, and the light beam 100 is incident on the electro-optic crystal 1. When an electric field 300 is generated between the electrodes 3 to be measured formed on the circuit board 2 to be measured, the electric field 300 causes a change in the physical state of the electro-optic crystal 1 to change the plane of polarization of the light beam 100. The electric field between the electrodes 3 to be measured can be detected by measuring the change in the plane of polarization. Depending on what material (crystal) is used as the electro-optic crystal 1, one that detects an electric field that is perpendicular to the circuit board 2 to be measured, that is, parallel to the optical axis of the light beam 100, and one that is parallel to the circuit board 2 to be measured. Some detect an electric field. FIG. 9 shows an example of detecting an electric field perpendicular to the circuit board 2 to be measured.

For details of the electric field detection probe, see, for example, Tadao Nagatsuma, "External EO Sampling Using Electro-Optical Crystal", Journal of the Institute of Electronics, Information and Communication Engineers, Vol. 75, no.
6, pp. 601-605, June 1992, Takeshi Kamiya, Ryo Takahashi, “Electro-Optical Sampling Using Semiconductor Laser as Light Source”, Applied Physics Vol. 61, No. 1, pp.
30-37, 1992.

However, in such a conventional structure, only a part of the leakage electric field from the circuit board 2 to be measured is electro-optical crystal 1.
However, there is a problem that the sensitivity is low because it is not applied to the sensor 3, the sensitivity changes due to the geometrical arrangement of the electrode 3 to be measured, and the absolute voltage cannot be measured.

FIG. 1 shows a conventional example that solves this problem.
0 and FIG. This conventional example is disclosed in JP-A-2-986.
No. 71 (hereinafter referred to as "prior application"), and is also cited in the Kamiya document mentioned above. This voltage measuring device is provided with a conductive transparent electrode 4 as an auxiliary electrode on the upper surface of the electro-optic crystal 1 and applies a variable voltage to the conductive transparent electrode 4. When the applied voltage is zero and the voltage V ₀ is applied to the measured electrode 3, an electric field in a direction perpendicular to the measured circuit board 2 is generated as shown in FIG. Occurs. Here, the voltage V _S is applied to the conductive transparent electrode 4 so that the polarization plane change is eliminated, that is, the electric field in the electro-optic crystal 1 is eliminated. This state is shown in FIG. Since there is no electric field in the electro-optic crystal 1, the voltage V _S applied to the conductive transparent electrode 4 should be equal to the voltage V ₀ of the measured electrode 3, and the absolute voltage of the measured electrode 3 can be measured. Becomes

Further, the prior application discloses an example in which an auxiliary electrode is provided on the side surface of the electro-optic crystal 1 and another voltage application method for measuring an absolute voltage.

[0007]

However, even with the technique disclosed in the prior application, it is necessary to calibrate each time in order to measure the absolute voltage, which is a problem in automating the measurement. .

An object of the present invention is to solve the above problems and to provide an electric field detecting device capable of measuring an absolute voltage without performing calibration.

[0009]

An electric field detecting device of the present invention has a shape that can be arranged in the vicinity of a circuit board to be measured, and an optical field from an electrode to be measured provided on the circuit board to be measured is used for optical detection. An element whose characteristics change, detection means for detecting a change in the physical state of light passing through this element, and an auxiliary electrode provided on at least one surface of this element,
The electric field detecting device including means for applying a voltage to the auxiliary electrode is characterized by including feedback means for controlling the voltage applied to the auxiliary electrode according to the output of the detecting means.

As the element whose optical characteristics change according to the electric field, in addition to the electro-optical crystal, a GaAs crystal whose absorption amount of light changes according to the electric field strength, a quantum well structure semiconductor, or the like can be used.

It is desirable that the control means includes means for controlling the voltage applied to the auxiliary electrode so that the change in the physical state of the light detected by the detection means is eliminated by the voltage application.

An element having a sensitivity to an electric field perpendicular to the circuit board to be measured is used as an element whose optical characteristics are changed by the electric field, and the auxiliary electrode is provided on the surface opposite to the surface of the element facing the circuit board to be measured. It is desirable to provide it.

The detecting means may further include means for modulating the voltage applied to the auxiliary electrode, and the detecting means may include means for synchronous detection using the modulation frequency of the means for modulating a change in the physical state of light.

In addition to the voltage applied to the auxiliary electrode, it is also possible to modulate the light incident on the element and use the modulation frequency for synchronous detection.

Pulsed light is used as the light incident on the element,
It is also possible to sample changes in the physical state of light.

[0016]

[Function] An auxiliary electrode is attached to at least one surface, preferably the upper surface, of an element whose optical characteristics are changed by an electric field.
A voltage is applied to the electrode in response to a change in the detected physical state when light is incident on this element. In particular, the voltage is applied so that the change in the physical state of light is not detected. The fact that no change in the physical state of light is detected means that no voltage is applied to the element, which means that the potential of the auxiliary electrode is equal to the potential of the measured electrode. Therefore, the voltage is equal to the voltage of the measured electrode, and the absolute voltage of the measured electrode can be measured without the need for calibration. Further, since a substantially constant electric field, usually a zero electric field, is always applied to the electric field detecting element, an output signal with good linearity can be obtained regardless of the linearity of the element.

When an element for detecting an electric field perpendicular to the circuit board to be measured is used as an element whose optical characteristics are changed by the electric field and an electrode is provided on the upper surface of the element, the geometrical shape of the electrode to be measured is used. The absolute voltage of the electrode can be measured regardless of the geometrical arrangement.

When the voltage applied to the element is modulated for synchronous detection, asynchronous noise can be removed, so that the signal-to-noise ratio is improved and the sensitivity is increased. In addition, since control is possible regardless of the power fluctuation of the light source, accurate absolute voltage can be measured.

When the light incident on the device is modulated, the light source A
It is possible to improve the signal-to-noise ratio while avoiding the influence of M noise.

Further, when the signal of the electrode to be measured is measured by sampling using pulsed light, the band required for the measuring means and the control means is sufficient as the band of the signal after sampling, so that it is independent of the band of the signal to be measured. It can be made low and easy to measure with a simple circuit. Also, the connection between the auxiliary electrode and the control means becomes simple. Further, since the noise bandwidth can be narrowed, the signal-to-noise ratio is improved and the sensitivity is increased. Also,
When the same measuring means and control means are used, the band of the electric field detection device can be made higher than that when continuous light is used.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows the configuration of an electric field detector according to the first embodiment of the present invention. Here, an example will be described in which a vertical electric field detection crystal, that is, an element that detects an electric field perpendicular to the circuit board 2 to be measured is used as the element whose optical characteristics are changed by the electric field.

The device of this embodiment has a shape that can be arranged in the vicinity of the circuit board 2 to be measured, and
The electro-optic crystal 1 is provided as an element whose optical characteristics are changed by the electric field from the electrode 3 to be measured, and the light source 5 is used as a detection means for detecting a change in the physical state of light passing through the electro-optic crystal 1. A structure including a polarizer 6, a wave plate 7 and a photodetector 8, a conductive transparent electrode 4 as an auxiliary electrode provided on at least one surface of the electro-optic crystal 1, and a structure capable of applying a voltage to the auxiliary electrode 4. Has become. Here, the feature of this embodiment is that a reference signal generator 9, a subtractor 10 and a control circuit are provided as control means for controlling the voltage applied to the conductive transparent electrode 4 according to the output of the photodetector 8. It is equipped with 11.

The electro-optic crystal 1 is sensitive to an electric field in a direction perpendicular to the circuit board 2 to be measured, and changes the plane of polarization of light propagating in parallel with the electric field direction. The light beam 100 output from the light source 5 passes through the polarizer 6, the wave plate 7 and the conductive transparent electrode 4, and enters the electro-optic crystal 1,
The light is reflected by the bottom surface of the electro-optic crystal 1, passes through the conductive transparent electrode 4 and the wave plate 7 again, and enters the polarizer 6. At this time, the polarization plane of the light beam 100 changes according to the voltage between the measured electrode 3 and the conductive transparent electrode 4. Polarizer 6
Reflects a specific polarization component of the reflected light from the electro-optic crystal 1, so that the amount of light incident on the photodetector 8 changes according to the change in the polarization plane of the light beam 100. That is, the output of the photodetector 8 changes according to the voltage between the measured electrode 3 and the conductive transparent electrode 4. The wave plate 7 is provided in order to adjust the offset amount of the light incident on the photodetector 8, and the waveplate 7 is provided to the photodetector 8 even when the voltage between the measured electrode 3 and the conductive transparent electrode 4 is zero. Inject a certain amount of light.

The output of the photodetector 8 is input to the subtractor 10. The subtractor 10 outputs the output of the photodetector 8 and the reference signal generator 9
The difference from the output of is output. The control circuit 11 uses the subtractor 1
A voltage is applied to the conductive transparent electrode 4 according to the output of 0.
At this time, the voltage of the conductive transparent electrode 4 is controlled so that the output of the subtractor 10 becomes zero. If the output of the reference signal generator 9 is made equal to the output of the photodetector 8 when the voltage between the measured electrode 3 and the conductive transparent electrode 4 is zero, the measured electrode 3 and the conductive transparent electrode are always transparent. The voltage between the electrodes 4 can be zero, that is, the measured electrode 3 and the conductive transparent electrode 4 can have the same potential. Therefore, if the voltage applied to the conductive transparent electrode 4 is taken out as the output signal 200, the voltage becomes equal to the voltage of the measured electrode 3.

FIG. 2 shows the configuration of the electric field detector of the second embodiment of the present invention. This embodiment is provided with an oscillator 12 and an adder 13 as means for modulating the voltage applied to the conductive transparent electrode 4, and the output of the photodetector 8 is provided at the modulation frequency from the oscillator 12 in the preceding stage of the control circuit 11. It differs from the first embodiment in that a lock-in amplifier 14 is provided as a means for performing synchronous detection using.

FIG. 3 is a diagram for explaining the operation of the second embodiment, where (a) is the amount of light incident on the photodetector 8 with respect to the voltage applied to the electro-optic crystal 1, and (b) is time on the horizontal axis. The output waveform of the taken oscillator 12, (c) is the photodetector 8 with respect to time
(D) shows the output waveform of the lock-in amplifier with the horizontal axis representing time, and (e) shows the output waveform of the lock-in amplifier 14 with respect to the voltage applied to the electro-optic crystal 1.

The amount of light incident on the photodetector 8 and the output of the photodetector 8 change depending on the voltage applied to the electro-optic crystal 1, as shown in FIG. Here, the wave plate 7
Is adjusted so that the amount of light incident on the photodetector 8 becomes zero when the voltage applied to the electro-optic crystal 1 is zero, that is, at point A in FIG. 3A.
In the oscillator 12, as shown in FIG. 3B, modulation is applied by ± ΔV. When this voltage is + ΔV, the photodetector 8
The amount of light incident on is at point B in FIG. 3A, and at −ΔV at point C. Since this characteristic is symmetrical with respect to the point A, the amounts of light incident on the photodetector 8 at the points B and C are equal. Therefore, the output of the lock-in amplifier 14 becomes zero as shown in FIG.

When the voltage applied to the electro-optic crystal 1 is positive, the amount of light incident on the photodetector 8 increases as the voltage increases, and the amount of light decreases as the voltage decreases. That is, the operating point is point A ′ in FIG. Therefore, the output of the photodetector 8 includes a component in phase with the output of the oscillator 12, as shown in the central portion of FIG. At this time, the output of the lock-in amplifier 14 outputs a positive voltage as shown in the central portion of FIG.

On the other hand, when the voltage applied to the electro-optic crystal 1 is negative, the operating point is point A ″ in FIG.
As the voltage increases, the amount of light incident on the photodetector 8 decreases. Therefore, the output of the photodetector 8 is
As shown on the right side of FIG. 3 (c), the output of the oscillator 12 includes a component of opposite phase. At this time, the output of the lock-in amplifier 14 outputs a negative voltage as shown on the right side of FIG.

As described above, the output of the lock-in amplifier 14 changes as shown in FIG. 3E with respect to the applied voltage of the electro-optical crystal 1, and when the applied voltage of the electro-optical crystal 1 is not zero, a positive / negative error occurs. Become a signal. Based on this error signal, the control circuit 11 controls so that the error signal becomes zero. That is, the voltage applied to the conductive transparent electrode 4 is controlled so that the voltage applied to the electro-optic crystal 1 becomes zero. By this control, the potential difference between the measured electrode 3 and the conductive transparent electrode 4 becomes zero. In this way, the same voltage as the measured electrode 3 can be obtained in the output signal 200.

When a direct current signal is used as a reference as in the first embodiment, in order to obtain positive and negative error signals, it is not possible to control the light incident on the photodetector 8 to a point where it becomes zero. Therefore, the power fluctuation of the light source 5 causes an offset error of the voltage applied to the conductive transparent electrode 4. On the other hand, in the second embodiment, since the point A where the light incident on the photodetector 8 is always zero is centered, the error due to the power fluctuation of the light source can be removed. Further, since the synchronous detection is performed, asynchronous noise is removed, the signal-to-noise ratio is improved, and the sensitivity is improved.

In FIG. 3, the modulation voltage applied to the conductive transparent electrode 4 is set to be smaller than the half-width voltage with the minimum light amount, but the invention is not limited to this and the modulation voltage can be arbitrarily selected. FIG. 4 shows a waveform example when the peak value of the modulation voltage is ½ of the half width voltage. In FIG. 4, (a) shows the amount of incident light on the photodetector 8 with respect to the voltage applied to the electro-optic crystal 1, and (b) shows the output waveform of the lock-in amplifier 14 with respect to the voltage applied to the electro-optic crystal 1. Show.

Although the output signal of the oscillator 12 is a rectangular wave here, any signal having a periodic waveform such as a sine wave or a triangular wave may be used.

FIG. 5 shows the structure of the electric field detecting device of the third embodiment of the present invention. In this embodiment, the output signal of the oscillator 12 is a sine wave, and the second harmonic of the modulation signal is used as the reference signal of the lock-in amplifier 14. That is, the output of the oscillator 12 is input to the frequency doubler 15, and the sine wave having the doubled frequency is input to the lock-in amplifier 14. The lock-in amplifier 14 synchronously detects the output signal of the photodetector 8 using the output of the frequency doubler 15 as a reference signal.

FIG. 6 shows the output of the photodetector 8 and the output of the lock-in amplifier 14 in the third embodiment. The horizontal axis is the voltage applied to the electro-optic crystal 1 together. As shown in FIG. 6B, the output signal of the lock-in amplifier is a second-order differential waveform of the output signal of the photodetector 8 shown in FIG. Therefore, if the output of the lock-in amplifier 14 is controlled to be zero, the slope of the output of the photodetector 8 becomes maximum with respect to the voltage applied to the electro-optic crystal 1 (point P in FIG. Controlled to be the operating point). Therefore, it is possible to eliminate the change of the control point due to the power fluctuation of the light source.

FIG. 7 shows the structure of an electric field detector according to the fourth embodiment of the present invention. In this embodiment, in order to avoid the influence of AM noise (mainly 1 / f noise) of the light source 5 and improve the signal-to-noise ratio, the polarization modulator 16 is used to modulate the light and the lock-in amplifier 14 is used. Synchronous detection is performed by. In this embodiment, both the incident light and the reflected light of the electro-optical crystal 1 are modulated, but it is also possible to adopt a configuration in which only the incident light is modulated.

FIG. 8 shows the structure of an electric field detecting device according to the fifth embodiment of the present invention. This embodiment is for detecting an electric field parallel to the circuit board 2 to be measured, and differs from the first embodiment in that a horizontal electric field detection crystal is used as the electro-optic crystal 1. The electro-optic crystal 1 differs from that of the first embodiment in that
It changes the plane of polarization of light propagating perpendicular to the direction of the electric field.
Light that is vertically incident on the electro-optic crystal 1 is reflected laterally on the side surface of the crystal, and is reflected on another side surface in the direction opposite to the incident direction. Therefore, an electric field perpendicular to the incident optical axis can be detected. Although the configuration equivalent to that of the first embodiment has been described here, the lateral electric field detection crystal can be used in any of the second to fourth embodiments by making the same modification.

In the above embodiments, a pulse light source may be used as the light source 5. In this case, since the signal of the circuit under measurement can be measured by the sampling method, the band of the photodetector 8, the control circuit 11 and the like can be lowered regardless of the band of the circuit under measurement, and the configuration is simple and its implementation is easy. . Also, since the noise bandwidth can be limited, the signal-to-noise ratio is improved and the sensitivity is improved. Further, when the same photodetector 8 and control circuit 11 are used, the band of the electric field detection device can be made higher than that when continuous light is used.

Although the wavelength plate 7 is used for offset adjustment in the above embodiments, this is not essential. Moreover, although the conductive transparent electrode is used as the auxiliary electrode, a metal electrode having an opening in a portion through which light is transmitted may be used. In addition to electro-optic crystals, GaAs crystals, which change the amount of light absorbed by the electric field strength, and quantum well structure semiconductors, are substances that change the physical state of light by electric fields, in addition to electro-optic crystals. The present invention can be similarly implemented using any one.

[0040]

As described above, the electric field detecting device of the present invention has a structure in which an electrode is provided on one surface of an element whose optical characteristics are changed by an electric field, and the electrode is controlled to have the same potential as the electrode to be measured. Therefore, the voltage equal to that of the measured electrode can be obtained, and the absolute voltage of the measured electrode can be measured without the need for calibration. Further, since a substantially constant voltage is always applied to the element for electric field detection, there is an effect that an output signal with good linearity can be obtained regardless of the linearity of the element.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of an electric field detection device according to a first embodiment of the present invention.

FIG. 2 is a diagram showing a configuration of an electric field detection device according to a second embodiment of the present invention.

FIG. 3 is a diagram for explaining the operation of the second embodiment, (a)
Is the incident light quantity of the photodetector with respect to the voltage applied to the electro-optic crystal, (b) is the output waveform of the oscillator with the horizontal axis of time, (c) is the output waveform of the photodetector with respect to time, (d)
Is the output waveform of the lock-in amplifier with time on the horizontal axis,
(E) is the output waveform of the lock-in amplifier with respect to the voltage applied to the electro-optic crystal.

FIG. 4 is a diagram showing an example of a waveform when a peak value of a modulation voltage is increased, (a) shows an incident light amount of a photodetector with respect to a voltage applied to an electro-optic crystal, and (b) shows an electro-optic crystal. Output waveform of lock-in amplifier with respect to applied voltage.

FIG. 5 is a diagram showing a configuration of an electric field detection device according to a third embodiment of the present invention.

FIG. 6 is a diagram showing a waveform example in the third embodiment,
(A) is the incident light amount of the photodetector with respect to the voltage applied to the electro-optic crystal, and (b) is the output waveform of the lock-in amplifier with respect to the voltage applied to the electro-optic crystal.

FIG. 7 is a diagram showing a configuration of an electric field detection device according to a third embodiment of the present invention.

FIG. 8 is a diagram showing the configuration of an electric field detection device according to a fourth embodiment of the present invention.

FIG. 9 is a diagram showing a configuration example of a conventional electric field detection probe and a measuring method thereof.

FIG. 10 is a diagram showing the configuration and operation of the voltage measuring device disclosed in the prior application, showing a state in which the conductive transparent electrode is grounded.

FIG. 11 is a diagram showing the configuration and operation of the voltage measuring device disclosed in the prior application, showing a state in which a voltage is applied to the conductive transparent electrode.

[Explanation of symbols]

 1 Electro-Optical Crystal 2 Measured Circuit Board 3 Measured Electrode 4 Conductive Transparent Electrode 5 Light Source 6 Polarizer 7 Wave Plate 8 Photodetector 9 Reference Signal Generator 10 Subtractor 11 Control Circuit 12 Oscillator 13 Adder 14 Lock-in Amplifier 15 frequency doubler 16 polarization modulator 100 light beam 200 output signal 300 electric field

Claims (6)

[Claims] 1. An element having a shape which can be arranged in the vicinity of a circuit board to be measured and whose optical characteristics are changed by an electric field from a measured electrode provided on the circuit board to be measured, and an element which passes through this element. An electric field detecting device comprising: a detecting means for detecting a change in a physical state of light; an auxiliary electrode provided on at least one surface of the element; and a means for applying a voltage to the auxiliary electrode. An electric field detecting device comprising a control means for controlling a voltage applied to the auxiliary electrode according to the output of the electric field detecting device. 2. The electric field according to claim 1, wherein the control means includes means for controlling the voltage applied to the auxiliary electrode so that the change in the physical state of the light detected by the detection means disappears when the voltage is applied. Detection device. 3. The element is an element having sensitivity to an electric field perpendicular to a circuit board to be measured, and the auxiliary electrode is provided on a surface of the element opposite to a surface facing the circuit board to be measured. The electric field detection device according to claim 1. 4. A means for modulating the voltage applied to the auxiliary electrode, wherein the control means includes means for synchronously detecting the output of the detecting means by using the modulation frequency of the means for modulating.
4. The electric field detector according to any one of 3 to 3. 5. The electric field detection according to claim 1, further comprising means for modulating light incident on the element, wherein the detecting means includes means for synchronous detection using the modulation frequency of the modulating means. apparatus. 6. The electric field detection device according to claim 1, wherein the light incident on the element is pulsed light, and the detection means includes means for sampling a change in a physical state of light.