TID and SEE characterization and damaging analysis of 256 Mbit COTS SDRAM for IEEM application

To map out device sensitivity with submicrometric resolutions it is traditional to use a microbeam. In recent years ion electron emission microscopy (IEEM) is emerging as an innovative method for device characterization. An advanced implementation of this instrument is under development at the SIRAD irradiation facility at the Legnaro national laboratory (LNL). The aim of this work is the final test and the characterization of the SIRAD IEEM in a realistic environment by using synchronus dynamic RAM (SDRAM) commercial off the shelf (COTS) devices to confirm the capability of the SIRAD IEEM to map out the single event effect (SEE) sensitivity of a typical microelectronic device and to measure its resolution. A potential problem during IEEM operations is the large number of ions that have to be collected on the device under test (DUT) that will induce a degradation of the device characteristics similar to that generated by total ionizing dose (TID). This paper investigates this issue and proposes an online method to monitor the degradation of the devices under test based on the measurement of the bit retention time (BRT), that is the time the information is retained in a memory cell without refresh in SDRAM devices. This paper presents the experimental setup and the results of TID and SEE tests performed to validate the method. The results of TID tests with ⁶⁰Co gamma ray, initially performed to investigate the method, show that BRT measurements could be used to online monitor the level of TID the device accumulates. The same tests performed during heavy ion irradiation show that ions produce similar effects on the SDRAM so that BRT could be used during IEEM operation to monitor the degradation of the DUT. TID and single event upset (SEU) effects have been investigated on Micron 256 Mb MT48LC64M4A2Y96A SDRAM devices at the ⁶⁰Co gamma facility of the Istituto per la Sintesi Organica e la Fotoreattivita and at the SIRAD irradiation facility at the - XTU Tandem of the INFN - CNR Legnaro National Laboratories (LNL).