JPH0731920B2 - Measuring method of programmable element - Google Patents

Description

TECHNICAL FIELD The present invention relates to a program element, and more particularly to a method for measuring output leakage current.

[Prior Art] Programmable elements are widely used because the marser can freely create desired logic elements.

However, at the time of manufacturing, it is necessary to ship in the final write state. Therefore, in addition to the memory cells used by the user, the function check memory cells written in advance at the time of manufacture can be installed, so that even in the final write state. It is devised so that it can be inspected.

[Problems to be solved by the invention]

The output leakage current, in which the output is placed in a high impedance state and the presence or absence of a leakage current is measured, is usually measured by selecting the write-in end cell. When the end write cell is selected, it is possible to measure the presence or absence of output leakage current, but if there is a leak current path in the current path used during writing, it may not be possible to detect it with end write cell selection. Output leakage current is detected for the first time after writing, resulting in writing failure, which reduces the writing yield, or output leakage current increases during use, which results in failure and reduces system reliability.

[Means for solving problems]

It is an object of the present invention to provide a measurement method capable of completely detecting output leakage current when manufacturing a programmable element.

The output leakage current measuring method of the present invention is a measuring method for detecting an output leakage current by selecting a written cell of a function check memory element that has been written at the time of manufacturing.

FIG. 2 is a configuration diagram of a programmable read only memory (hereinafter referred to as PROM) which is a type of conventional programmable element. Reference numeral 1 is an X-side decoder, 2 is a Y-side decoder used for reading, and 3 is a current drive circuit used for writing. Reference numeral 4 is an output circuit, and 5 is a CS circuit for controlling activation and deactivation of the output circuit. Ten
Is the current path from the output to the current drive circuit, Qmn
(M = 1,2, n = 1,2) is a memory cell used by the user.

The output leakage current is measured by deactivating the output from the CS input and detecting the presence or absence of the output leakage current path. The following two paths can be considered as the current path of the output leakage current. First, if the output circuit itself has a current path, this allows the leakage current to be detected regardless of the state of the selected memory cell.
The other is when there is a leakage current path in the current drive circuit of 3.

In this case, if the selected memory cell is a final write, it functions as a diode in the direction opposite to the direction of the leakage current, so that the current path is blocked and the output leakage current cannot be detected. In this case, the output leakage current is detected only after the writing is actually performed, and it becomes a defect after shipping, and the reliability is apparently lowered.

〔Example〕

 Next, the present invention will be described with reference to the drawings.

FIG. 1 is an embodiment of the present invention and is a block diagram of a PROM.

1 is an X-side decoder, 2 is a Y-side decoder at the time of reading, 3 is a current driving circuit used at the time of writing, Qmn is a memory cell used by the user, 4 is an output circuit, 5 is a CS circuit, and It has the same structure as the PROM. In the conventional example, the output leakage current was measured without using the function-checking memory cells 11 and 12 having memory cells written in advance at the time of manufacture, but in the measuring method of the present invention, 11 and 12 are turned ON. By selecting the written cells of all the digit lines of the memory cells for function check, it is possible to detect the leakage current path in the current drive circuit 3 which cannot be detected in the final write. At this time, a write path 10, a written cell of all digit lines of the memory cell for checking the function of the current drive circuit 3, and a leak current path through the X-side decoder are formed, and detection is possible. The function check memory cell can be selected by applying a larger voltage to A ₀ A ₁ at the TTL level.

〔The invention's effect〕

As described above, the present invention is
The output leakage current that could not be detected can be detected, the quality of the programmable element can be greatly improved, and the effect is great. In the present invention, a bipolar PROM is taken as an example,
It goes without saying that the same effect can be obtained with other programmable elements.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of the present invention. Figure 2 shows
It is a figure which shows a prior art example. Q _{11 to} Q ₄₄ …… Program element.

Claims (1)

[Claims] 1. A programmable element having electrically writable memory cells and having function checking memory cells including memory cells written at the time of manufacturing in advance.
When measuring the output leakage current, select the programmed memory cells of all digit lines of the function check memory cells,
A measurement method is characterized in that the output leakage current flowing from the output terminal to the digit line through the current drive circuit for writing data is measured while the data output circuit is inactivated.