MRAM vs SRAM vs DRAM: A Detailed Comparison

This article compares MRAM, SRAM, and DRAM, highlighting the differences between these memory types.

MRAM stands for Magnetoresistive RAM, SRAM stands for Static RAM, and DRAM stands for Dynamic RAM. RAM, of course, stands for Random Access Memory.

MRAM (Magnetoresistive RAM)

MRAM memory states

MRAM is a type of RAM that utilizes magnetic elements, rather than electron charge (as in semiconductor memories), to store data. It leverages electron spin, which is inherently permanent. This makes MRAM a compelling option, combining the speed of SRAM, the density of DRAM, and the non-volatility of flash memory. As such, it’s often touted as the “ideal memory.”

MRAM working

The architecture of a classical MRAM is depicted above. Each bit is stored within a spin-dependent tunnel junction memory cell, accessed via magnetic row and column write lines. The spin-dependent tunnel junction exhibits a significant change in resistance based on the predominant electron spin within a storage layer.

The tunnel barrier is extremely thin, just a few atomic layers. Its behavior depends on spin polarization; electrons can tunnel through this normally insulating material, causing a change in resistance. Therefore, in MRAM, data is read by measuring the tunnel junction resistance, while data is stored in the spin polarization of a magnetic layer within the tunnel junction.

The write lines generate magnetic fields that set the magnetic spin polarization, thereby storing the data bits. Conventionally, the low resistance state represents logic-0, while the high resistance state represents logic-1.

In summary:

• Magnetic cells store the data.
• Reading is accomplished by measuring the resistance of the cell. The magnetic tunnel effect modifies the cell’s resistance based on the magnetic field orientations in the surrounding plates.
• Writing can be achieved in several ways. The initial method involved using induced magnetic fields to alter the fields of the plates. Writing techniques have since evolved, depending on the application and available resources.

MRAM implementation involves several underlying methods and technologies, including:

• Toggle mode
• Spin-transfer torque
• Thermal assisted switching

Future generations of MRAM technology aim to further reduce cell size and power consumption.

SRAM (Static RAM)

SRAM-Static RAM

• SRAM stands for Static Random Access Memory.
• Static RAM is implemented using an array of storage cells.
• Information is stored in latches.

Key features of an SRAM storage cell:

• SR Latch
• Select input for control
• Dual Rail Data: Inputs B and B
• Dual Rail Data: Outputs C and C

DRAM (Dynamic RAM)

DRAM-Dynamic RAM

• DRAM stands for Dynamic Random Access Memory.
• Its fundamental principle is storing information on capacitors. Due to charge leakage, periodic refreshing of the charge is necessary.
• The stored value is changed by charging and discharging the capacitor.
• A transistor acts as a “switch” to store, charge, or discharge the capacitor.

DRAM variants include:

• Synchronous DRAM (SDRAM)
• Double Data Rate DRAM (DDR DRAM)
• RAMBUS DRAM (RDRAM)

Comparison Between MRAM, SRAM, and DRAM

The following table compares MRAM, SRAM, and DRAM memory types.

MRAM vs SRAM: Key Differences

• MRAM is slightly slower than SRAM, though still competitive in speed.
• SRAM has a more complex design, whereas MRAM offers higher density.
• MRAM is non-volatile, while SRAM is volatile and loses data without power.

MRAM vs DRAM: Key Differences

• MRAM offers faster read/write speeds compared to DRAM, which relies on capacitor charging/discharging.
• MRAM and DRAM feature similar densities.
• MRAM is non-volatile, unlike DRAM.
• MRAM exhibits lower cell leakage.
• MRAM has lower voltage requirements than DRAM, which requires frequent data refreshing.