Design Article
Memory 101: What you need to know about FRAM, part 2
2/15/2013 1:29 PM EST
Looking ahead
The existing FRAM manufacturers have successfully balanced their ferroelectric compositions, electrodes, passivation layers, process flows, and circuit designs to create useful non-volatile memory. That memory is especially suited for embedded applications. Ferroelectric capacitors are fully static so they exhibit approximately the same hysteresis loop independent of frequency down to the sub-hertz range, making them perfectly suited for inclusion in fully static CMOS designs that operate over a range of clock speeds or stop their clocks to save energy. This appears to be the niche that FRAM is creating for itself, not as non-volatile memory but as main memory in the low power circuits demanded for new hand-held, wireless, remote, and energy-harvesting products.
There are thousands of known ferroelectric materials, and more are discovered continually. Most ferroelectric materials are mixtures of two or more metal oxides, leading to thousands of additional variations within each ferroelectric material family. The electrical and reliability properties of each distinct ferroelectric composition change for different electrode types, expanding the universe of choices further. Consequently, the ferroelectric designer has a near infinite selection of memory capacitor structures from which to choose, although the vast majority of this landscape remains unexplored. Now that the FRAM has established itself commercially and ferroelectric microcircuits can be built profitably, the quest for improvement inherent in the integrated circuit industry will eventually exploit all of the potential of this technology. The memory effect of ferroelectric materials is intrinsic at all size scales from centimeters to nanometers, both laterally and vertically, making possible unique products outside the historical IC memory regime. Given the low energy consumption, wide speed range, and non-volatility of ferroelectric-based memory, the technology may soon be found in unexpected places.
References and notes
1. The method for accomplishing this read/restore operation is the basis for the fundamental architecture patent for FRAMs. Thanks to our complex patent system in the United States, that fundamental patent was recently re-issued and has another 18 years before expiration even though it was first submitted in 1987. That patent is now owned by Cypress Semiconductor, which recently acquired Ramtron. Ramtron lost a major battle with National Semiconductor over this very patent but ended up with National’s version in a settlement, National having originally acquired the patent by purchasing Krysalis long ago. The Krysalis 512ECD was the first implementation of that architecture.
2. J. Evans and R. Womack, “An experimental 512-bit nonvolatile memory with ferroelectric storage cell,” IEEE Journal of Solid-State Circuits, 23[5], pp 1171-1175 (Oct 1988).
3. P. Larsen, G. Kampschöer, et al., “Ultrafast polarization switching of lead zirconate titanate thin films,” Proceedings of the IEEE 8th Symposium on Applications of Ferroelectrics, Greenville, N.C., USA; pp 217-224 (Aug 1992).
4. N. Abt, R. Moazzami, and Y. Nissan-Cohen, “Anomalous remanent polarization in ferroelectric capacitors,” Integrated Ferroelectrics, 2[1-4], pp121-131 (1992).
About the author
Joe
T. Evans, Jr., is president of Radiant Technologies Inc. (Albuquerque,
NM), which manufactures test equipment for measuring ferroelectric,
piezoelectric and pyroelectric properties. The company also fabricates
integrated thin-film piezoelectric and ferroelectric products as
embedded references in its test equipment. Joe earned a B.S. in
electrical engineering as a Distinguished Graduate from the United
States Air Force Academy in 1976. Upon completing undergraduate pilot
training, he served as a flight instructor in the supersonic T-38 Talon.
After earning an MS in electrical engineering from Stanford University,
Joe was assigned to the Air Force Weapons Laboratory. He left the Air
Force in 1984 and co-founded Krysalis Corp., becoming the first to
create thin ferroelectric films on silicon substrates and in 1987
fabricating the first fully functional CMOS ferroelectric random access
memory. He subsequently co-founded Radiant Technologies, Inc. in 1988
and has worked on a variety of issues in ferroelectric materials since
that time including FRAM, ferroelectric capacitor reliability, and
piezoelectric MEMs. His present goal is to create useful form factors
for thin-ferroelectric-film capacitors so engineers can use these
devices in circuits and ICs.
Acknowledgement
I would like to acknowledge the contribution by the following people for their review of and suggestions for this article: Richard Womack of Rio Grande Micro; Glen Fox of Fox Materials Consulting; and Bob Howard, Spencer Smith, Scott Chapman, and Michelle Bell, all of Radiant Technologies Inc.
Related articles:
Industry View: Objective Analysis on Cypress, Ramtron
Alternative NVM technologies require new test approaches, part 2
Top 5 memory trends for 2013
Non-volatile memory development gathers steam
The existing FRAM manufacturers have successfully balanced their ferroelectric compositions, electrodes, passivation layers, process flows, and circuit designs to create useful non-volatile memory. That memory is especially suited for embedded applications. Ferroelectric capacitors are fully static so they exhibit approximately the same hysteresis loop independent of frequency down to the sub-hertz range, making them perfectly suited for inclusion in fully static CMOS designs that operate over a range of clock speeds or stop their clocks to save energy. This appears to be the niche that FRAM is creating for itself, not as non-volatile memory but as main memory in the low power circuits demanded for new hand-held, wireless, remote, and energy-harvesting products.
There are thousands of known ferroelectric materials, and more are discovered continually. Most ferroelectric materials are mixtures of two or more metal oxides, leading to thousands of additional variations within each ferroelectric material family. The electrical and reliability properties of each distinct ferroelectric composition change for different electrode types, expanding the universe of choices further. Consequently, the ferroelectric designer has a near infinite selection of memory capacitor structures from which to choose, although the vast majority of this landscape remains unexplored. Now that the FRAM has established itself commercially and ferroelectric microcircuits can be built profitably, the quest for improvement inherent in the integrated circuit industry will eventually exploit all of the potential of this technology. The memory effect of ferroelectric materials is intrinsic at all size scales from centimeters to nanometers, both laterally and vertically, making possible unique products outside the historical IC memory regime. Given the low energy consumption, wide speed range, and non-volatility of ferroelectric-based memory, the technology may soon be found in unexpected places.
References and notes
1. The method for accomplishing this read/restore operation is the basis for the fundamental architecture patent for FRAMs. Thanks to our complex patent system in the United States, that fundamental patent was recently re-issued and has another 18 years before expiration even though it was first submitted in 1987. That patent is now owned by Cypress Semiconductor, which recently acquired Ramtron. Ramtron lost a major battle with National Semiconductor over this very patent but ended up with National’s version in a settlement, National having originally acquired the patent by purchasing Krysalis long ago. The Krysalis 512ECD was the first implementation of that architecture.
2. J. Evans and R. Womack, “An experimental 512-bit nonvolatile memory with ferroelectric storage cell,” IEEE Journal of Solid-State Circuits, 23[5], pp 1171-1175 (Oct 1988).
3. P. Larsen, G. Kampschöer, et al., “Ultrafast polarization switching of lead zirconate titanate thin films,” Proceedings of the IEEE 8th Symposium on Applications of Ferroelectrics, Greenville, N.C., USA; pp 217-224 (Aug 1992).
4. N. Abt, R. Moazzami, and Y. Nissan-Cohen, “Anomalous remanent polarization in ferroelectric capacitors,” Integrated Ferroelectrics, 2[1-4], pp121-131 (1992).
About the author
Joe
T. Evans, Jr., is president of Radiant Technologies Inc. (Albuquerque,
NM), which manufactures test equipment for measuring ferroelectric,
piezoelectric and pyroelectric properties. The company also fabricates
integrated thin-film piezoelectric and ferroelectric products as
embedded references in its test equipment. Joe earned a B.S. in
electrical engineering as a Distinguished Graduate from the United
States Air Force Academy in 1976. Upon completing undergraduate pilot
training, he served as a flight instructor in the supersonic T-38 Talon.
After earning an MS in electrical engineering from Stanford University,
Joe was assigned to the Air Force Weapons Laboratory. He left the Air
Force in 1984 and co-founded Krysalis Corp., becoming the first to
create thin ferroelectric films on silicon substrates and in 1987
fabricating the first fully functional CMOS ferroelectric random access
memory. He subsequently co-founded Radiant Technologies, Inc. in 1988
and has worked on a variety of issues in ferroelectric materials since
that time including FRAM, ferroelectric capacitor reliability, and
piezoelectric MEMs. His present goal is to create useful form factors
for thin-ferroelectric-film capacitors so engineers can use these
devices in circuits and ICs.Acknowledgement
I would like to acknowledge the contribution by the following people for their review of and suggestions for this article: Richard Womack of Rio Grande Micro; Glen Fox of Fox Materials Consulting; and Bob Howard, Spencer Smith, Scott Chapman, and Michelle Bell, all of Radiant Technologies Inc.
Related articles:
Industry View: Objective Analysis on Cypress, Ramtron
Alternative NVM technologies require new test approaches, part 2
Top 5 memory trends for 2013
Non-volatile memory development gathers steam
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