Technical Field
The present disclosure relates to memory devices such as a semiconductor memory, and method for testing reliability of memory devices.
Related Art
In general reliability tests on semiconductor memories, a testing device is used to write and read data to and from all regions in a memory array with a known test pattern, and the data written to the memory array by the testing device (expected value) is compared with the data read from memory array by the testing device, so as to check the reliability of the memory array.
In pre-shipment inspection of semiconductor memories, in order to reduce a testing cost, reliability test is generally performed concurrently on multiple semiconductor memories, by connecting multiple semiconductor memories to one testing device and writing and reading data to and from the multiple semiconductor memories with a common test pattern.
With semiconductor memories provided with a pseudo-random number generator for improving security, random number values of pseudo-random numbers are predictable, and thus multiple semiconductor memories can generate an identical pseudo-random number by using a common algorithm. Pre-shipment inspection can therefore be conducted concurrently on multiple semiconductor memories with one testing device, in the same way as on general semiconductor memories.
Random number generators are cryptographic technology employed for a wide variety of uses in many security systems.
Random numbers generated by random number generators are used for, for example, key information in a cryptographic algorithm, or authentication codes for mutual authentication between devices, and are closely related to the security strength of a system and thus highly confidential information.
Random numbers generated by random number generators therefore need to be highly random. At shipment of semiconductor devices provided with a random number generator, a random number test is normally performed to evaluate whether a random number generator generates random numbers that meet a required level.
JP2005-517998A and WO2005/124537A describe a technique to evaluate whether the frequencies of appearance of “0” and “1” in random numbers generated by a random number generator are within an allowable range.