ULTRARAM™
Technology
ULTRARAM™
Tech Overview
ULTRARAM™ is a remarkable, patented, memory technology developed by Lancaster University. It exploits a quantum-mechanical process called resonant tunnelling, allowing ULTRARAM™ to deliver non-volatility with fast and energy-efficient write and erase, resulting in high endurance. This combination of properties was thought to be unachievable until now. ULTRARAM™ has the non-volatility of flash, with a performance that is expected to exceed that of DRAM.
The $165bn pa memory market is dominated by dynamic random-access memory (DRAM, $100bn) and NAND flash ($60bn). Flash is non-volatile, retaining data when unpowered, but is slow and has poor program/erase cycling endurance. In contrast, DRAM is fast with excellent endurance, but it is volatile, and requires data to be constantly refreshed. For decades there has been a quest for a memory that combines their advantages without their disadvantages, i.e. a memory that is fast and non-volatile, with high endurance and ultra-low switching energies; a so-called ‘universal memory’. ULTRARAM™ has achieved these universal memory characteristics.
Explainer Video
Quantum Technology
ULTRARAM™
ULTRARAM™ is a flash-like floating-gate memory. However, unlike flash, which uses a highly-resistive oxide barrier to retain charge in the floating gate, ULTRARAM™ uses atomically-thin layers of InAs/AlSb to create a triple-barrier resonant-tunnelling (TBRT) charge-confining structure. The TBRT switches between a highly-resistive (locked) state (with no bias, ‘store’), to a highly-conductive (unlocked) state on application of just 2.5 V across the gate stack (program/erase). It is this mechanism that gives ULTRARAM™ its remarkable properties.
Quantum Technology
ULTRARAM™
ULTRARAM™
Unlike DRAM and flash, which are silicon based, ULTRARAM™ uses III-V compound semiconductors. Specifically, the so-called 6.1-angstrom family of semiconductors (GaSb, InAs and AlSb). This allows engineering of the memories’ electrical properties to exploit the underlying physics to full effect, whilst also being capable of volume manufacture using established processes in the compound semiconductor and silicon industries. The extremely low electron-effective-mass in InAs also opens the possibility for a new high-speed embedded III-V logic to address arrays.
Energy Efficiency
The factors determining energy efficiency vary widely for different memory technologies. For example, many emerging memories function by making/breaking interatomic bonds or by switching atomic magnetic moments. These processes are energy intensive, resulting in high program/erase energies. Charge based memories such as flash and DRAM are superior in this respect as they manipulate electrons rather than atoms, which requires less energy. However, there is still room for even greater efficiency!
With its combination of low capacitance and low voltage program/erase, ULTRARAM™ has a switching energy per unit area that is 100x lower than DRAM, 1,000x lower than flash and over 10,000x lower than other emerging memories. ULTRARAM™’s ultra-low energy credentials are further enhanced by its non-destructive read and non-volatility, which removes the need for refresh.
Program Erase / Switching Energies
10,000 x
Lower than other emerging memories
100 x
Lower than DRAM
Program Erase / Switching Energies
1,000 x
Lower than Flash
ULTRARAM™
High Endurance
Endurance refers to the number of times a memory cell can be programmed/erased before it is worn-out. This is a weakness of non-volatile memories such as flash, which typically only withstand 10,000 program/erase cycles. In contrast, ULTRARAM™ has demonstrated degradation free operation in excess of 10 million program/erase cycles. This is due to the low-voltage, ultra-low-energy program/erase process enabled by quantum resonant tunnelling.
Non-Volatility vs Speed
A memory is non-volatile if it is able to retain data when unpowered, requiring a robust logic state that is difficult to change, e.g. flash. In contrast, a fast memory seemingly requires the logic state to be frail so that it can be changed quickly and easily, e.g. DRAM. Therefore, a memory that is fast and non-volatile seemingly requires contradictory physical properties and has long been dismissed as unachievable.
ULTRARAM™ breaks this paradigm through the use of quantum mechanics and resonant tunnelling. Extrapolated retention times in excess of 1,000 years have been demonstrated and scaling of devices down to state-of-the-art feature sizes is predicted to achieve speeds that match or exceed DRAM.
ULTRARAM™
EXTREME DATA RETENTION
ULTRARAM has a flash-like structure. The presence of electrons in a floating gate determines the logic state of the memory, i.e. whether it is storing a 1 or a 0. To be classed as non-volatile the memory must be able to retain this charge for extended periods whilst unpowered.
In the absence of an applied voltage the triple-barrier resonant-tunnelling structure (TBRT) is highly insulating. Therefore, the floating gate is electrically isolated, and the electrons are trapped.
This makes ULTRARAM non-volatile – even when unpowered it can store data for over 1,000 years.
In the absence of an applied voltage the triple-barrier resonant-tunnelling structure (TBRT) is highly insulating. Therefore, the floating gate is electrically isolated, and the electrons are trapped.
This makes ULTRARAM non-volatile – even when unpowered it can store data for over 1,000 years.
Retention
Retention
HIGH-SPEED PROGRAM/ERASE
AT ULTRA-LOW ENERGY
HIGH-SPEED
PROGRAM/
ERASE AT
ULTRA-LOW
ENERGY
Program/Erase
Program/Erase
ULTRARAM™
HIGH SPEED AND ULTRA-LOW ENERGY
ULTRARAM™ uses the power of quantum mechanics to achieve ultra-low energy program/erase at DRAM-like speeds.
The application of a small, 2.5 V, control gate voltage unlocks the TBRT, allowing electrons to flow into the floating gate, programming the memory cell. Electron flow occurs by quantum-mechanical resonant-tunnelling, which is extremely fast.
The removal of the gate voltage locks the TBRT, trapping the electrons. By applying a 2.5 V control gate voltage with the opposite polarity, the TBRT once again unlocks, but electrons flow in the opposite direction, erasing the memory cell.
The combination of small program/erase voltages, short pulse durations and the intrinsically low capacitance of the memory cell allows ULTRARAM to achieve DRAM-like speeds with a switching energy per unit area that is lower than any other memory technology.
The application of a small, 2.5 V, control gate voltage unlocks the TBRT, allowing electrons to flow into the floating gate, programming the memory cell. Electron flow occurs by quantum-mechanical resonant-tunnelling, which is extremely fast.
The removal of the gate voltage locks the TBRT, trapping the electrons. By applying a 2.5 V control gate voltage with the opposite polarity, the TBRT once again unlocks, but electrons flow in the opposite direction, erasing the memory cell.
The combination of small program/erase voltages, short pulse durations and the intrinsically low capacitance of the memory cell allows ULTRARAM to achieve DRAM-like speeds with a switching energy per unit area that is lower than any other memory technology.
Program/Erase
Program/Erase
ULTRARAM™
HIGH SPEED AND ULTRA-LOW ENERGY
ULTRARAM™ uses the power of quantum mechanics to achieve ultra-low energy program/erase at DRAM-like speeds.
The application of a small, 2.5 V, control gate voltage unlocks the TBRT, allowing electrons to flow into the floating gate, programming the memory cell. Electron flow occurs by quantum-mechanical resonant-tunnelling, which is extremely fast.
The removal of the gate voltage locks the TBRT, trapping the electrons. By applying a 2.5 V control gate voltage with the opposite polarity, the TBRT once again unlocks, but electrons flow in the opposite direction, erasing the memory cell.
The combination of small program/erase voltages, short pulse durations and the intrinsically low capacitance of the memory cell allows ULTRARAM to achieve DRAM-like speeds with a switching energy per unit area that is lower than any other memory technology.
The application of a small, 2.5 V, control gate voltage unlocks the TBRT, allowing electrons to flow into the floating gate, programming the memory cell. Electron flow occurs by quantum-mechanical resonant-tunnelling, which is extremely fast.
The removal of the gate voltage locks the TBRT, trapping the electrons. By applying a 2.5 V control gate voltage with the opposite polarity, the TBRT once again unlocks, but electrons flow in the opposite direction, erasing the memory cell.
The combination of small program/erase voltages, short pulse durations and the intrinsically low capacitance of the memory cell allows ULTRARAM to achieve DRAM-like speeds with a switching energy per unit area that is lower than any other memory technology.
ULTRARAM™
NON-DESTRUCTIVE READOUT
The logic state of ULTRARAM memory is read by measuring the conductance of an underlying channel. The channel conductance is dependent on the logic state of the memory: If electrons are present in the floating gate (logic state 0) they repel electrons in the channel and the conductance is low. If the floating gate is empty (logic state 1) the channel conductance is high.
This readout method is non-destructive, which means that unlike DRAM, the logic state of the memory is preserved after read and doesn’t need to be re-written. This greatly reduces the complexity and energy consumption of ULTRARAM memory chips.
This readout method is non-destructive, which means that unlike DRAM, the logic state of the memory is preserved after read and doesn’t need to be re-written. This greatly reduces the complexity and energy consumption of ULTRARAM memory chips.
READOUT
READOUT
