JPS61258400A - Nonvolatile semiconductor storage device - Google Patents

Abstract

PURPOSE:To measure directly the transistor characteristics of a memory cell obtained after writing, by using a control circuit which applied the voltage of a program power supply system to a word line of the memory cell and can select only the current supplied to the memory cell to flow it to a power supply and then setting a control mode for said control circuit. CONSTITUTION:For a control circuit having the circuit constitution where three memories are selected by an EPROM, a signal 12 is set at a high level with a signal 8 turned off respectively. Thus no current is flowed from a program power supply. While a signal 14 is set at a low level and it is possible to supply the voltage that can cover a voltage range required to obtain the voltage Vth through V-I measurement to a node 9 since a transistor 6 is depressed. Then no current flows to other circuits on a CD basis owing to CMOS. Therefore, the above-mentioned state is set for measurement of the program power supply voltage and the current flowed from a lead power supply to secure square characteristics. Then voltage/current characteristics can be obtained as shown in the diagram. As a result, the voltage Vthp can be measured directly after programming of the EPROM with high reproducibility and high accuracy within 0.1V.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention provides a method for programming an internal memory and then determining the post-program threshold voltage (hereinafter referred to as Vthp) of the internal memory cell.
The present invention relates to a non-volatile semi-difficult memory (referred to as Di EFROM) that has made it possible to measure EFROM.

[Summary of the invention]

In the present invention, after writing data to a memory cell of an MPROM, in the means for measuring vth after writing, current does not flow to any other than the written memory cell, and a high voltage is applied to the word line. This allows Vthp, which rarely reaches a high value, to be accurately and directly measured by measuring voltage-current from an external terminal.

[Conventional technology]

Conventionally, in EPROM, v of a memory cell after programming is
Accurately measuring th is considered important in selecting non-defective EFROMs or in reliability tests. Until now, maximum operating voltage (hereinafter referred to as VCCm
There is a known method of measuring Vccmax (referred to as aX) and converting the measured Vccmax to vth after cooling. Here, when the vth of the memory cell after writing becomes 8 to 10 V or higher and is used at 5 V, the memory cell does not turn on because the word line voltage is 5 V or lower. Therefore, the memory data is determined by increasing vth.

When the operating voltage is increased, the word line voltage increases. For example, if the vth of the memory cell has risen to 8V, if the operating voltage is increased above 8V, the memory cell will be turned on and the data in the memory will be reversed. If the operating voltage is increased by 8V or more due to data inversion, lP
Reading data from the ROM will result in a malfunction. Therefore, the voltage at which the memory cell is turned on at the maximum operating voltage,
That is, it is possible to know vth after writing.

[Problems and Objectives to be Solved by the Invention] However, the conventional method of calculating Vth after writing by converting Vccmaz is There is. t ta v
Since ccmaX is determined via the sense amplifier system, it is difficult to narrow down its accuracy to within α5V depending on the presence or absence of a slight charge in the sense amplifier system when the memory cell is turned on. Furthermore, since the operating voltage is a lead power supply system, the withstand voltage is around 10 to 12 V, so it becomes impossible to measure when vth is close to ICM7.

The conventional technology has such problems. Therefore, in order to solve these conventional problems, the present invention has the following features:
The purpose of this method is to directly measure the transistor 41 of the memory cell after it has been assembled, and to directly and accurately measure the Vthp of the memory cell from the two-sided curve, and also to make it possible to measure even high vthp.

[Means for solving problems]

In order to solve the above problems, in a nonvolatile semiconductor memory device that stores data by increasing the threshold voltage of the memory cell, a program power supply system voltage is applied to the word line of the memory cell, and the current flowing through the power supply is applied to the memory cell word line. The present invention is characterized in that a control circuit that allows only current to flow in the control circuit and a mode for controlling the control circuit are set.

[Effect]

In the KFROM configured as above, if the terminal is set to the program state and the pledge data is 71, the program power supply voltage and the read current flowing to the read power supply are measured and the two-side characteristics are taken, it is possible to directly select the selected memory. It is possible to measure Vthp after writing to the cell, and since the program power supply has a high withstand voltage, it is possible to measure up to a high Vthp.

〔Example〕

The present invention will be explained below with reference to Examples. Figure j1!1 shows an embodiment of the present invention. 1 is a program power supply, 2 is a read power supply, 3 is ]]'AMOS memory cell, 4 and 5 are N
6 indicates an Nch depletion transistor, and 7.8 indicates a pch) transistor.

9 is the node 10.11. ．． 12°13.14 indicate signal lines. Here, if the control circuit with the circuit configuration shown in FIG. 1 is set as an example of the mode of the present invention in which the memory selected in the lPROM is 3, in FIG.
The signal becomes Hlgh, and the signal 8 turns OFF. As a result, no current flows from the program power supply. Further, the signal at 14 is set to Lo, but since the transistor at 6 is a degreaser, it is possible to supply a voltage to node 9 that can cover the voltage range necessary to obtain vth by means of -2-constructive measurement. Since the current is 0MO3 in other circuits, no current flows in the other circuits. Therefore, when the above state is set and the current flowing from the program power supply voltage and the read power supply is measured and two-sided characteristics are obtained, voltage-current characteristics as shown in FIG. 2 are obtained. According to this measurement, in which the intercept point of the straight line to the X-axis in FIG. 2 is vth after programming, good reproducibility and accuracy of Q and 1v or less can be obtained. It is also possible to measure 7thp of 20v or more.

In addition, the modes that can be set include the mode in which the word line can be set to VPP in the read mode, and the mode in which the word line can be set to VPP in the read mode, and the mode in which the word line can be set to VPP in the program mode. A mode that can set non-memory cells to standby state as an IF, etc. No current other than memory cells flows to the bit line and V to the word line.
Many mode settings are possible in which pp-based voltage can be applied.

〔Effect of the invention〕

As explained above, the present invention directly adjusts Vthp after programming in lPROM to 0.1 with good reproducibility.
It can be measured with an accuracy within V, and even higher Vthp can be measured.

[Brief explanation of the drawing]

*1S is an E'FROM memory cell selection and write/read switching circuit diagram in one embodiment of the present invention. Second
The figure is a voltage-current characteristic diagram measured by the present invention. 1...Program power supply 2...Read power supply 5...? AMOS memory 7.5...1...Nch) transistor......Nch depressing transistor 7
......pch transistor 9...node 10.11.12, 13.14...signal line 15...sense amplifier Fig. 1 Fig. 2

Claims (1)

[Claims] In a nonvolatile semiconductor memory device that stores data by increasing the threshold voltage of a memory cell, a control circuit that applies a program power supply voltage to the word line of the memory cell and reduces the current flowing to the power supply only to the current flowing to the memory cell. and a mode for controlling the control circuit.