"Radiation Tolerant and Intelligent Memory for Space“ T. Dargnies 1 , J. Herath 2 , T. Ng 2 , C. Val 1 , J.F. Goupy 1 , and J.P. David 3 1 3D PLUS 2 NASA Langley Research Center 3 ONERA 2005 MAPLD International Conference September 7-9, 2005 Washington DC. Contents Introduction
"Radiation Tolerant and Intelligent Memory for Space“
T. Dargnies1, J. Herath2, T. Ng2, C. Val1, J.F. Goupy1, and J.P. David3
1 3D PLUS2 NASA Langley Research Center
2005 MAPLD International Conference
September 7-9, 2005
512 Mb SDRAM
512 Mb SDRAM
Interface and SDRAM controller FPGA
48 (data bus)
512 Mb SDRAM
512 Mb SDRAM
512 Mb SDRAM
512 Mb SDRAM
2. Preliminary design / heritage / radiation assessment
Previous 3D PLUS memory modules for space applications have embedded ELPIDA (former HITACHI) SDRAMs. In fact, 3D PLUS has a long history and significant experience with the 512 Mb monolithic die EDS5108ABTA which has been fully characterized versus TID (CO60 TID characterization) and SEE. This experience and knowledge is why this particular memory was chosen as the basis for this design.
Simplified schematic of the module
Note1: Each active component is also protected with a specific thermal shutdown (over current protection) component.
Note2: Internal CLK = 100 MHz (SDRAM operation).
Note3: All components and signals are not represented in this simplified schematic.
Note:1 Test performed by ONERA at Toulouse (France), 2 Test performed by RAD at TAMU (USA), 3 Test performed by 3D PLUS at TAMU (USA)
Let’s focus on the three main and critical components tested under radiation effects (EEPROM radiation characteristics are guaranteed by Xilinx Datasheet because purchased in space quality level.
3.1 Xilinx XQ2V1000 FPGA Radiation results / SEL Testing
SEL Testing at Texas A&M University
The Xilinx FPGA showed no SEL events at LETs of 86.6MeV-cm2/mg (normal incidence irradiation) and at 124MeV-cm2/mg (effective LET at 45-degrees angle of incidence irradiation). Each irradiation was performed to a total effective fluence of 1E7ions/cm2).
3.2.1 ELPIDA EDS5108ABTA SDRAM Radiation results (TID)
CO60 TID Testing up to 50Krad(Si)
Conclusion: SDRAM is within specifications at 50 Krad(Si)
3.2.2 SDRAM Radiation results (SEL / SEU / SEFI)
Heavy Ions Testing up to 74 MeV/mg.cm²
SEL X-Section as a function of LET
In addition, the SDRAM memories showed no SEL events at LETs of 40, 60, and 80MeV-cm2/mg at a temperature of 85ºC. Test was performed at higher temperatures and the parts showed no SEL events at a LET of 80MeV-cm2/mg at temperatures of 85, 100 and 125ºC.
3.3.1 Voltage Regulator Radiation results (TID)
CO60 TID Testing up to 15Krad(Si)
Conclusion: Voltage Regulator is within specifications at 10 krad (Si)
3.3.2 Voltage Regulator Radiation results (SEL / SET)
Heavy Ions Testing up to 60 MeV/mg.cm²
SEE Testing conclusion:
This component show Single Event phenomenon at LET of 86.6 MeV.cm²/mg and ambient temperature. A high internal current is observed after an unexpected shutdown of the output voltage of the part.This unexpected shutdown of the regulator may be the consequence of the impact of ions on the digital part of the die that embed the automatic thermal shutdown and other electronics.
No SEL is observed at both LET of 60 MeV.cm²/mg and 86.6 MeV.cm²/mg, however, at these LET, Single Event Transients are observed on the output voltage .
4. Design completion
Figure 1 : Dose Vs Al thickness for Geosynchronous orbit
TID requirement is 100 Krad(Si). Based on Figure 1 simulation results and components testing TID results, we added specific shielding on components. Epoxy resin HYSOL FP4450 (density = 1.77 g/cm3) is the moulding resin used by 3D PLUS. With AutoCAD software and design file of the module, minimum thickness of epoxy resin around a component in X, Y and Z axis is calculated. When required extra Tantalum (density = 16.6 g/cm3) shielding is added on parts.To manage the TID requirement, we added 250 µm of Tantalum on all the active parts (3 axis protection) except for TPS75715 and MAX803 components (750 µm).
Three dimensional calculations performed by 3D PLUS for each active component permits to conclude that 100 krad(Si) requirement for a Geosynchronous Orbit and a mission duration.
Picture 2: After final shielding (top)
Picture 1: Before final shielding (top)
Prototypes have been manufactured and tested in April 2005. First results are very promising (see pictures 1, 2 & 3).
The part electronically behaves as planned. Embedded software (VHDL written for test), permits simulation of SDRAM Single Event Upsets to check that the mitigation system operates as intended.
Picture 3: After final shielding (bottom)
5. Prototypes results / functional validation
3D PLUS, in partnership with NASA LaRC, designed and manufactured the first high density and fast access time SRAM-like memory module (1Gb or 2Gb available) TID tolerant to 100 krad (Si) and SEE immune up to 60 MeV/mg.cm².
The real improvement of this brand-new memory is the significantly reduced board design time (no complex controller, no SEU management, no TID management required anymore). This module is to be directly connected to a processor or equivalent and considered as a radiation tolerant device.
Related paper: Presentation of Tak-kwong Ng and Jeffrey Herath of NASA LARC on hardware and software design of this module (A208).
7. Author Information
Corresponding (and Presenting) Author:
Timothée Dargnies, 3D PLUS, 641 rue H. Boucher 78532 Buc (France), phone : +33 1 30 83 26 56, fax: +33 1 39 56 25 89, email: firstname.lastname@example.org
Jeff Herath, NASA LaRC, Mail Stop 488, Hampton VA23681 (USA), phone : +1 757 864 1098, email : email@example.com
Tak-kwong Ng, NASA LaRC, Mail Stop 488, Hampton VA23681 (USA), phone : +1 757 864 1097, email : firstname.lastname@example.org
Christian Val, 3D PLUS, 641 rue H. Boucher 78532 Buc (France), phone : +33 1 30 83 26 51, fax: +33 1 39 56 25 89, email: email@example.com
Jean Francois Goupy, 3D PLUS, 641 rue H. Boucher 78532 Buc (France), phone : +33 1 30 83 26 53, fax: +33 1 39 56 25 89, email: firstname.lastname@example.org
Jean-Pierre David, ONERA, Complexe scientifique 2 avenue E. Belin, 31055 Toulouse Cedex (France), phone : + 33 5 62 25 27 37, email : email@example.com