Magnetoresistive Element Additive Work Function Bias Voltage
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Solution Overview
Problem
Current magnetoresistive random access memory (MRAM) devices face challenges in achieving a steep dependence of the magnetoresistance ratio (MR ratio) on bias voltage, which is necessary for efficient reading and writing operations, as the MR ratio is high at low voltages for reading and low at high voltages for writing.
Innovation Solution
Incorporating an additive element with a work function smaller than the concentration-weighted average of the main component in the ferromagnetic layers, specifically with a difference of 0.3 eV or more, to create a steep dependence of the MR ratio on bias voltage by adjusting the energy barrier height and width of the tunnel barrier layer, allowing for reduced write voltage and maintained read voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the MR ratio is increased for high-speed reading, then reading speed is improved, but writing voltage increases causing energy loss
Solution Approach 1:
The patent applies parameter changes by introducing an additive element (Mg, Al, Ca, Sc, Ti, V, Mn, Zn, As, Sr, Y, Zr, Nb, Cd, In, Ba, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, or Lu) into the ferromagnetic layer with a work function difference of 0.3 eV or more from the main component. This changes the energy band structure and density of states at the Fermi level, enabling the MR ratio to decrease with increasing bias voltage. Consequently, the device achieves high MR ratio at low reading voltages while maintaining low MR ratio at high writing voltages, resolving the contradiction between reading speed and writing energy consumption
Solution Approach 2:
The patent implements dynamics by creating a voltage-dependent MR ratio characteristic where the MR ratio dynamically changes with bias voltage. The additive element induces a steep negative slope in the MR ratio vs. bias voltage curve, allowing the device to automatically adapt its resistance characteristic based on the applied voltage level. This dynamic behavior enables high read efficiency at low voltages while reducing write energy requirements at high voltages
2Manufacturing precision
If the barrier resistance is increased for data writing, then writing precision is improved, but write voltage increases
Solution Approach 1:
The patent changes the parameter of barrier resistance by introducing the additive element into the ferromagnetic layer. This modifies the density of states and energy band alignment at the tunnel barrier interface, creating a barrier resistance that is highly dependent on bias voltage. The additive element causes the barrier resistance to decrease with increasing voltage, enabling high writing precision at moderate voltages while preventing excessive voltage requirements
3Productivity
If the dependence of MR ratio on bias voltage is made steep, then operating efficiency is improved, but device complexity increases
Solution Approach 1:
The patent achieves a steep dependence of MR ratio on bias voltage through parameter changes in the material composition. By adding a small concentration of additive element (5-50 at%) with appropriate work function difference, the device obtains the desired steep MR ratio voltage dependence without complex structural modifications. This maintains manufacturing simplicity while achieving high operating efficiency
Solution Approach 2:
The patent creates a composite ferromagnetic layer by combining the main component (Co, Fe, Ni or their alloys) with additive elements having different work functions. This composite structure leverages the electronic structure differences between elements to achieve the steep MR ratio voltage dependence, obtaining enhanced operating efficiency through material composition rather than structural complexity
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach results in a magnetoresistive effect element with a steep dependence of the MR ratio on bias voltage, enabling lower write voltages while maintaining high read voltages, thus optimizing the operating conditions for MRAM devices.
Implementation Method 1
it has become possible to obtain a very high magnetoresistance ratio (MR ratio) of 100% or more by the tunnel magnetoresistive effect (TMR effect) in a ferromagnetic tunnel junction including a sandwiched structure in which a tunnel barrier made of MgO is inserted between two ferromagnetic layers made of CoFeB
Implementation Method 2
data is written to a large-capacity MRAM by supplying a write current to the MTJ element, and switching the magnetization direction in the storage layer by the spin-transfer torque method
Data Source
AI summary
A magnetoresistive effect element includes the following structure. A first ferromagnetic layer has a variable magnetization direction. A second ferromagnetic layer has an invariable magnetization direction. A tunnel barrier layer is formed between the first and second ferromagnetic layers. An energy barrier between the first ferromagnetic layer and the tunnel barrier layer is higher than an energy barrier between the second ferromagnetic layer and the tunnel barrier layer. The second ferromagnetic layer contains a main component and an additive element. The main component contains at least one of Fe, Co, and Ni. The additive element contains at least one of Mg, Al, Ca, Sc, Ti, V, Mn, Zn, As, Sr, Y, Zr, Nb, Cd, In, Ba, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Hf, Ta, and W.