Messi Biology stated that in the era of information explosion, data requires faster access and longer retention. Magnetoresistive Random-Access Memory (MRAM) is precisely a new type of memory that combines high-speed read/write capabilities, non-volatility (retaining data when power is cut), and nearly unlimited write endurance. A critical enabler pushing MRAM toward industrialization is an ultrathin magnesium oxide (MgO) film measuring only 1 to 2 nanometers thick. Though invisible and intangible, it determines whether MRAM can truly achieve “fast computing and reliable memory.”
The core storage unit of MRAM is called the Magnetic Tunnel Junction (MTJ), which has a “sandwich” structure: a very thin insulating barrier layer sandwiched between upper and lower ferromagnetic layers (typically cobalt-iron-boron). MRAM records 0s and 1s based on the “parallel” or “anti-parallel” alignment of the magnetic moments of the upper and lower magnetic layers. To move from one layer to the other, electrons must “tunnel” through the intermediate insulator—and this insulator is the domain of magnesium oxide. Early tunnel junctions used amorphous aluminum oxide (Al₂O₃), which yielded a room-temperature magnetoresistance ratio of only a few dozen percent, limiting signal identification capability. In 2001, theoretical physicists predicted that substituting an ordered (001)-oriented single-crystal magnesium oxide barrier could potentially push the magnetoresistance ratio beyond 1000%. By 2004, experimental teams achieved nearly 200% in Fe/MgO/Fe structures, followed shortly by the advent of CoFeB/MgO/CoFeB structures. MgO subsequently replaced aluminum oxide to become the standard barrier material for modern spintronic devices.
The “magic” of magnesium oxide lies in its crystal structure. Magnesium oxide features a standard cubic rock-salt structure. When grown as a single crystal in the (001) direction, its lattice resembles a regularly arranged “sieve.” Electrons with different spin states face vastly different difficulties when passing through this sieve—electrons in the parallel state pass through almost unimpeded, while those in the anti-parallel state are largely reflected. This “spin-filtering effect” drastically amplifies the resistance difference of the MTJ between the two magnetization states, generating a massive Tunneling Magnetoresistance (TMR) ratio.
The higher the TMR ratio, the easier it is for the chip to distinguish between “0” and “1,” resulting in a lower error rate for read signals and faster speeds. In other words, MRAM’s read/write speed and reliability heavily depend on the purity, density, and lattice integrity of this magnesium oxide film. Achieving a defect-free single-crystal film with a thickness of 1–2 nanometers requires a material purity of 4N (99.99%) level, a standard that ordinary industrial magnesium oxide cannot fulfill.
Fabricating this ultrathin film relies on magnetron sputtering technology, where high-energy ions bombard a magnesium oxide target, “depositing” atoms one by one onto the wafer. For a long time, high-quality magnesium oxide sputtering targets were monopolized by a few foreign manufacturers such as those in Japan, representing a lingering bottleneck in China’s MRAM industrial chain. A turning point arrived in August 2025, when a Suzhou-based enterprise announced the successful development of its self-developed 6-inch MRAM-MgO target. With a purity of 4N, a density exceeding 99.8%, and grain uniformity reaching international advanced standards, this breakthrough filled a critical link where the localization rate was previously close to zero. Combined with previously localized targets such as cobalt-iron-boron, platinum-manganese, and ruthenium, all functional layers of the magnetic tunnel junction achieved domestic independent supply for the first time, truly eliminating the risk of overseas supply cutoffs.
From physical principles to engineering implementation, the story of magnesium oxide in MRAM is a vivid footnote on how materials science can propel an entire industry. With the successive opening of domestic magnesium oxide targets, specialized etching equipment, and mass-production lines, MRAM is transitioning from laboratories into real-world scenarios such as industrial control, automotive electronics, and edge computing. That paper-thin layer of magnesium oxide is becoming the foundation and confidence for domestic memory chips to enter the global arena.