The NVM Insider, Issue 11 - Page 4 - Tech Tidbits

Tech Tidbits: 1T-OTP Test Features to Support In-Field Programmability

Craig Downing, Product Marketing Manager, Sidense

Sidense 1T-OTP is ideally suited to a broad range of applications and provides many benefits for many use cases, including security, reliability and cost-effective implementation. Its flexibility allows it to be used as a ROM or eFuse replacement supporting programming during manufacture and test. In addition many applications require programming of all or a part of the array in the field - for example supporting devices that allow firmware code revisions, security key updates or device configuration and adjustment.

In all cases, support for a comprehensive test methodology for the OTP memory is important to provide high reliability for manufactured devices. In general, testing the circuitry to access bit-cell contents, such as the sense amplifiers, word-line and bit-line drivers, will provide coverage for this critical circuitry in an OTP macro. For applications where bit-cell contents are programmed at manufacture and test, the test program may also include a method for verifying that the desired bits are correctly and reliably programmed. As programming OTP results in a one-way, permanent structural change within the bit-cell, a program-verify cycle during test will allow weakly programmed bits to be detected and corrected.

For applications that require the OTP to be field programmable, the situation is not as straightforward. As the device will be partially, completely or incrementally programmed in the field (for example for emulated multi-time-programming or eMTP), a method is required for testing the macros before the cells are programmed. 1T-OTP has many advantages over other forms of NVM when used as eMTP or field-programmable memory, and includes the ability to test macros with un-programmed cells.

All Sidense 1T-OTP macros, provide a rich set of test features that include the following:

• Sense amplifier testing
• Bit-line and Word-line testing
• Built-in cell margin modes for program-verify
• Bit-cell level testing of un-programmed bits to identify any marginal bit-cells

Sidense 1T-OTP macros generally include some spare memory spaces where individual bits can be programmed during test, without adversely affecting the available memory space in the field, thus allowing the programming circuitry to be fully exercised. These features provide reliable test coverage for devices that will be programmed in the field. Additionally, the program-verify method ensures that when programmed, the desired bit-cell contents are programmed correctly. Sidense 1T-OTP also supports a number of read-modes, including redundant mode which can be used to further improve reliability for field-programming applications.

All test and programming steps can be performed at wafer level, after packaging at final or system test, or in the field. Incremental programming of the OTP can be done throughout all test levels and in the field. As a further advantage of Sidense's 1T-OTP, neither high-temperature wafer bake nor packaged part burn-in is required, making it a very flexible, reliable and cost-effective solution compared to other types of NVM.

Detailed application notes are available from Sidense describing the test features and test methodology for different applications and use cases.