Researchers report on a conception of a design, modelling, fabrication and room-temperature operation of a novel, low-voltage, compound-semiconductor, charge-based, non-volatile memory device with a compact form.
Whilst the different forms of conventional (charge-based) memories are well suited to their individual roles in computers and other electronic devices, flaws in their properties mean that intensive research into alternative, or emerging, memories continues. In particular, the goal of simultaneously achieving the contradictory requirements of non-volatility and fast, low-voltage (low-energy) switching has proved challenging.
Static random access memory (SRAM), dynamic random access memory (DRAM) and Flash have complementary characteristics that make them well-suited to their specialised roles in cache, active memory and data storage, respectively. Nevertheless, each of them have their drawbacks. Writing and erasing of Flash memories requires application of a large voltage to the control gate (CG). The process is slow, and is limiting the endurance of the device. On the other hand, only small voltages are needed to read the data by testing the conductivity of the channel. This is efficient, and leaves the data intact, which is known as non-destructive read.
In contrast to Flash, all DRAM single bit operations are relatively fast, making it the workhorse of active memory. However, data is lost from DRAM cells when it is read. Furthermore, charge leaks from the capacitors used to store the data, so DRAM also has to be refreshed every few tens of ms.
These issues mean that despite the evident long-standing success of conventional memories, the search for alternatives, so-called emerging memories, continues unabated. Charge trap memory, phase change memory, ferroelectric RAM, resistive RAM, conductive bridge RAM and magnetoresistive RAM, collectively called storage-class memory (SCM) are all examples of emerging memories which have been subject to vigorous research activity.
In a paper published on Nature, researchers describe a" Universal Memory" that combines the advantages of both DRAM and flash storage without their drawbacks.
The researchers used quantum mechanics to avoid the trade-off between stability, long-term data storage and low-energy writing/erasing.
Specifically, they describe an oxide-free, floating-gate memory cell based on III-V semiconductor heterostructures with a junctionless channel and non-destructive read of the stored data. Non-volatile data retention of at least 104 s in combination with switching at ≤2.6 V is achieved by use of the extraordinary 2.1 eV conduction band offsets of InAs/AlSb and a triple-barrier resonant tunnelling structure. The device is a FG memory structure made of InAs/AlSb/GaSb heterostructures, with InAs used as both FG and the junctionless channel.
The combination of low-voltage operation and small capacitance implies intrinsic switching energy per unit area that is 100 and 1000 times smaller than dynamic random access memory and Flash respectively. The device may thus be considered as a new emerging memory with considerable potential.
Their paper includes simulations to demonstrate the device operation concept, while the key memory properties of the new memory device, such as the retention characteristics of the programmed/erased states, are presented as experimental results on fully-operational single cell devices.
This new computer memory could immediately reduce peak power consumption in data centers by one-fifth. If implemented successfully in the future, Universal Memory could replace both the DRAM as well as flash drives.