Japanese

VLSI Design and Test

Today, we use a programing language (Hardware Description Language, HDL) to design LSI (Hardware) like software. However, electronic data of hardware design are finally transformed into physical circuits by manufacturing process. That is an important difference in terms of reliability. In case of hardware, even if electronic circuits (designs) before manufacturing are completely correct, some physical circuits manufactured from the designs might be faulty.

It is inevitable that some manufactured LSIs are faulty. Therefore, the process to identify good LSIs and faulty LSIs is required. This process is called LSI testing. Testing is an essential process to ship out highly dependable LSIs.

What is testing? Testing consists of the following two processes.

Test generation is the process of generating input patterns and their expected responses to test a circuit. Test application is the process of applying test patterns to the circuit, observing the responses and comparing them with the expected responses. If some response is different from the expected response, the circuit is identified to be faulty.

Current LSIs consists of hundreds of millions of signals and gates, and therefore, the test generation is complicated and time consuming process. In addition, test application targets all the manufactured LSIs, and hence it requires a terribly long time. Consequently, the ratio of test cost over whole manufacturing costs increasing, and innovation of test technology has being required.

In Dependable System Laboratory, we are tackling several challenges on VLSI testing as follows.