JPH06249913A - Jig for measurement of low current - Google Patents

Abstract

PURPOSE:To achieve a low noise by a method wherein a conductive guard which surrounds an element to be measured and a connecting cable is installed and the potential of the guard is controlled to be identical to the potential of an electrode from which a current to be measured flows out. CONSTITUTION:A guard 30 is attached to a lower-part member 2 via insulating spacers 31, 32, and it is fixed mechanically to the member 2 so as to be electrically insulated. A guard 33 forms a pair with the guard 30, and it is connected mechanically and electrically to the guard 30 by conductive thumscrews 34, 35. In addition, both of the guards 30, 33 are insulated electrically from an upper-part member 3 or the member 2. The guard 30 is connected electrically to an upper-part terminal for a standoff terminal 15 in a point 19 so that it becomes the same potential as an internal shield 11 for a measuring cable. When a measuring hig (JUG) constituted in this manner is used, the high- accuracy measurement of a very small current can be performed with good operability.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a current measuring device, and more particularly to a measuring jig used for measuring a very small current.

[0002]

2. Description of the Related Art As electronic devices have become more sophisticated and have higher performance, it has become increasingly important to measure minute currents in order to measure the characteristics of those electronic devices. In particular, with the miniaturization of semiconductor devices and the reduction in power consumption, it is not uncommon to be required to measure a current below the pA order in order to judge the quality of the semiconductor devices.

In many minute current measuring systems, such as when measuring the leakage current of a device under test (hereinafter referred to as DUT) such as a semiconductor device, a measuring jig to which the DUT is attached for measurement and a jig for the measuring jig are mounted on the jig. A current measuring device (hereinafter CMU) that is connected and measures, displays, or outputs the measured current.
That is) and has a configuration having.

The current input terminal pairs of the CMU are usually arranged to realize a virtual short circuit, and the outside of the input terminal pairs is shielded by an outer conductor, and the outer conductor is normally forced to the ground potential. . A device for introducing a measured current from the measured part of the DUT to the current input terminal pair of the CMU with low noise, stability, and good workability is a measuring jig (hereinafter referred to as JIG).
It is the role of).

FIG. 2 is a perspective view showing the appearance of such a JIG 1. The lower member 2 and the upper member 3 made of a conductive material are rectangular troughs and have a space inside, and the hinge 7 provided on the back surface 6 serves as a fulcrum to open and close the upper member 3 in the direction of the double arrow 5. can do. Also, the measurement cable 4-
1, 4-2, 4-3, 4-4 is not limited to four, but is introduced into the internal space of the lower member 2 through the respective openings provided in the front surface 2-1 of the lower member 2, It consists of a DUT mounted inside to input the measured output current to an external CMU and a DUT to which a voltage or current is applied. In FIG. 2, the lower member 2 and the upper member 3 may be covered with an insulating material such as vinyl to improve the appearance.

FIG. 3 is a side sectional view of the JIG 1 shown in FIG. 2, in which a conductive cable and the like are drawn in perspective in part. The current measurement cable 4-2 includes a core wire 10, an inner shield 11 that surrounds the core wire 10 with an insulator, an outer shield 12 that surrounds the inner shield 11 with an insulator, and is electrically connected to the lower member 2. The core wire 10 and the inner shield 11 are connected to the through-type standoff terminals 14 and 15 attached to the lower member 2 via the relay coaxial wire 13, respectively.
It extends to the pins 18a and 18b of the mounting socket 18. The socket 18 is a high-insulation insulator attached to the lower member 2 and has pins 18a, 18b, etc. planted thereon.
The electrodes of the UT 20 are electrically connected to the pins 18a, 18b and the like, and are mechanically supported. The external insulators of the standoff terminals 14 and 15 and the insulator of the socket 18 are made of Teflon or the like with high insulation and low loss.

The current is measured after raising the front surface of the upper member 3 to expose the upper surface of the lower member 2 and mounting the DUT 20 in the socket 18 and then closing the upper member 3. The structure of the JIG 1 must be mechanically strong, and the electrical connection between the upper member 3 and the lower member 2 must be kept good.

The relay cable 13 may be extended as it is to reach the pins 18a and 18b of the socket 18. In this case, the core wire 1 through which the measured current flows
Normally, the potential difference between 0 and the inner shield 11 is set to be substantially zero, and only the current from the internal element of the DUT 20 connected to the pin 18a (generating the current to be measured) is supplied to the pin 18a. Pin 18b or another adjacent pin 18c to the pin 18a (when the connection is completed because the pin 18c and the pin 18b are not connected in the figure), the pin 1
Leakage of current to 8a is prevented.

However, the potential of the pin 18a and the potential of the upper member 3 are generally different and have a potential difference of V volt with each other. If the stray capacitance between the pin 18a and the conductor 16 and the upper member 3 and the lower member 2 is C farad, the charge Q Coulomb is accumulated between them.
Therefore, due to the change of the above variable,
A noise current I amp expressed by the following equation is generated. I = dQ / dt = V (dC / dt) + C (dV / dt) where dQ / dt, dC / dt and dV / dt are the time derivatives of Q, C and V, respectively.

Even if the applied voltage V is kept constant, a current is generated when the stray capacitance C changes. It is generally J
It results from mechanical deformation of IG1. For example, assuming that V is 10 V and C is sine wave oscillated at 50 Hz with an amplitude of 0.001 picofarad, the amplitude of the noise current due to the change of C is 3.14 picoampere. It is difficult to prevent such a minute change in capacitance.

Even in the measurement of a field effect device integrated on a semiconductor wafer, which is an industrially useful application, the influence is particularly large on a substrate having a large area.

[0012]

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a conductive guard surrounding a device to be measured in a JIG used for measuring a small current to reduce noise and solve the above problem.

[0013]

SUMMARY OF THE INVENTION In order to achieve the object of the present invention, a conductive guard surrounding a device to be measured and a connection cable is provided in a current measuring state, and the potential of the guard is equal to the potential of an electrode through which the current to be measured flows. Controlled to the same. Therefore, the V becomes almost 0 volt (practically, a voltage of several millivolts remains), and the induced current becomes extremely small. Further, since the guard shields a portion having a potential different from that of the electrode through which the measured current flows out from the electrode, an effect that the size of the capacitance C becomes extremely small can be obtained.

[0014]

1 is a sectional view of a JIG 100 according to an embodiment of the present invention, which is similar in appearance to FIG. 2 and 3
The elements having the same functions as in 1 are given the same reference numerals.

JIG1 and JIG100 in the prior art
One of the differences is that the guards 30 and 33 are provided. The guard 30 includes a lower member 2 and an insulating spacer 3
It is attached via 1, 32, and is mechanically fixed to the lower member, but is electrically insulated.
The guard 33 is paired with the guard 30 and is mechanically and electrically connected to the guard 30 by conductive thumbscrews 34 and 35 during current measurement. Both the guards 30 and 33 are electrically insulated from both the upper member 3 and the lower member 2. Guard 30
Is also electrically connected to the upper terminal of the standoff terminal 15 as shown at point 19 so that it has the same potential as the inner shield 11 of the measuring cable. In addition,
A leaf spring having a thin conductor is inserted between the guard 33 and the guard 30 as illustrated. In the drawing, the space between the guard 33 and the guard 30 is exaggerated for the purpose of clearly showing the spring.

FIG. 4 shows another embodiment of the present invention in which the conductors 16 and 17 in FIG. 1 are replaced with a coaxial cable 36. The core wire of the coaxial cable 36 is the DUT pin 18
a and the core wire 10 of the measurement cable 4-2 are connected, and the outer cover is connected to the guard 33 and the pins 18b and 18c of the DUT. The advantage of this embodiment is that it is possible to shield between the conductor 16 and the part having the potential difference. It is preferable to apply such a coaxial cable to other measurement cables, and it is also preferable to shield other conductor portions having a potential different from that of the electrode through which the measured current flows.

FIG. 5 shows another embodiment of the present invention in a sectional view similar to FIG. In this embodiment, the guard 33 is mechanically fixed to the upper member 3 by screws 53 and 54 while being electrically insulated via the insulating washers 51 and 52. A metallic pin 55 is planted in the guard 33 so as to be electrically connected to the opening 56 provided in the guard 30. In this embodiment, raising the upper member 3 has the advantage that the DUT 20 is immediately exposed.

In FIG. 5, a further switch 37 is provided.
The purpose is to match the potentials of the guards 30 and 33 with the potential of the inner shield of the measurement cable for measuring the current. If the CMU connected to the cable 4-2 is in the measurement state, the switch 37 is closed; otherwise, the CMU connected to another measurement cable (for example, the cable 4-1) is connected.
When the MU is in the measurement state, the switch that connects the inner shield of the cable 4-1 and the guard 30 is closed, and the switch 37 is opened.

As described above, the portion having a potential different from that of the conductor portion through which the current to be measured flows can be effectively shielded, so that the noise current is effectively suppressed. Of course, those skilled in the art can easily infer that the opening and closing of the switch 37 and the like can be automatically controlled from the outside by using a relay.

In the above embodiment, the measuring cable 4-2 is used.
The relay cable 13 and the coaxial cable 36 are relayed by the standoff terminals 14 and 15.
3 and the coaxial cable 36 may be directly connected, or may be connected via a connector. In that case, the outer shield conductor of the cable is electrically connected to the guards 30 and 33.

[0021]

As described above in detail, the use of the JIG of the present invention is advantageous because high precision measurement in minute current measurement can be performed with good workability. Generally, the difference between the potentials of the guards 30 and 33 and the potential of the electrode through which the measured current flows can be about 1 millivolt, so
Compared to the conventional example that generated a potential difference of about 0 V,
A signal-to-noise ratio improvement of about 0 times is achieved. In addition, in the above-mentioned embodiment of the present invention, the upper member 3 and the lower member 2
Also works as an insulator.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view of a low current measuring jig according to an embodiment of the present invention.

FIG. 2 is a perspective view of a conventional low-current measuring jig and a low-current measuring jig according to an embodiment of the present invention.

FIG. 3 is a schematic cross-sectional view of the conventional low current measurement jig of FIG.

FIG. 4 is a schematic sectional view of a jig for measuring low current according to another embodiment of the present invention.

FIG. 5 is a schematic sectional view of a jig for measuring low current according to still another embodiment of the present invention.

[Explanation of symbols]

 1,100: JIG (Jig for low current measurement) 2: Lower member 3: Upper member 4-1, 4-2, 4-3, 4-4: Measurement cable 5: Opening and closing direction of upper member 3 6: Back of JIG 7: Hinge 18: Socket 18a, 18b, 18c: Socket pin 20: DUT 30, 33: Guard 34, 35: Thumbscrew 36: Coaxial cable 37: Switch 51, 52: Insulation washer 53, 54: Screw 55: Metal pin 56: Opening for receiving the pin 55

Claims (3)

[Claims] 1. A device to be measured for generating a current to be measured is mounted, and an output terminal composed of first, second and third conductors insulated from each other for outputting the current to be measured to a current measuring instrument is provided. A measuring jig, comprising a conductor for introducing the first conductor and for confining the element to be measured substantially in a closed space, being biased to the same potential as the first conductor. A guard connected to the second conductor, and a ground connected to the third conductor,
A jig for low current measurement, wherein the first conductor is electrically connected to a predetermined portion of the element to be measured, and the current to be measured is output from the portion. 2. The jig for measuring low current according to claim 1, wherein the third conductor is extended so as to substantially surround the guard. 3. A first and a second elements to be measured, which generate currents to be measured, are mounted, and the first and second currents to be measured are respectively output to a current measuring device, which are insulated from each other. A measuring jig having first and second output terminals made of second and third conductors, each of which has an inlet for the first conductor and substantially closes the device under test. Consists of a conductor for confining
The first output terminal of the first output terminal is selectively biased to the same potential as the first conductor of the second output terminal or the same potential of the first conductor of the second output terminal of the biased output terminal. A guard connected to the second conductor, a ground connected to at least one of the third conductors, and a switch for connecting the second conductor of the energized output terminal to the guard. And a low current that electrically connects the first conductor of the biased output terminal to a predetermined portion of the device under test and outputs the measured current from the region. Measuring jig.