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Insulators and Metal Layers by Single Growth Cycle

Application of ferromagnetic insulating thin films in portable electronics requires that the film is homogeneously magnetized. In laboratory this is achieved by applying an external magnetic field by large electromagnets. This is clearly impractical in hand-held electronics, and we developed an in-situ processing technique in which the ferromagnetic insulator is converted into a strong ferromagnetic conductor with a large remnant magnetization. Subsequent ferromagnetic insulator layer(s) with excellent lattice matching between the layers are grown as desired.

 

Lattice matching is critical for high-quality multilayer
structure devices with good interlayer magnetic coupling

 

We do not need separate techniques to grow dielectric and metal layers. Instead the insulating layer is converted to a strong ferromagnetic conductor - called the biasing layer - in such a way that the positions of atoms responsible for the magnetic properties remain sufficiently intact. The magnetic atom array in the subsequently grown insulating layer continues the magnetic atomic array of the biasing layer. Below is a magnetic hysteresis loop measured from a double layer structure, total thickness is 40 nm. The contributions from the biasing layer and the insulating layer (estimated from the data collected on the layer possessing no biasing layer) are given. Due to the strongly magnetized biasing layer the coercive field is significantly different from zero, which guarantees that the insulating layer stays magnetized.

Despite strong magnetization, the structure has no rare-earth elements or iron.

Magnetic characteristics of a permanently magnetized double-layer structure manufactured by our technology. The double-layer structure has a very high-quality interface between the layers.

 

We can provide solutions for versatile applications operating also at and above room temperature:

(i) Combinations of insulating ferromagnetic layers with different coercive fields

(ii) Combinations of conducting ferromagnetic layers with different coercive fields

(iii) Combinations of i and ii with high-quality interfaces

(iv) Processing routes required in items i-iii

 

The processing temperatures are low, varying for different stages between 300 and 500°C

 

Low-temperature solutions by direct electrode writing based on material conversion (see below, mask-less patterning) are achievable. Crystalline films grow also below 500°C, which is a benefit with delicate circuits.

 

Why should manufacturers and developers pay attention - what we do differently

Conventional patterning of ferromagnetic layers involves a growth of different materials on the film (top electrodes), or on the substrate followed by a growth of ferromagnetic layer (bottom electrodes).

 

Our solution is versatile - we convert the desired layers or
portions of layers into a conducting ferromagnetic form

 

Besides conventional vertical devices, this opens a route to
manufacture planar devices, such as spin filters and spin valves

 

Layer structures are applied in magnetic field sensors, spin filters and spin valves. Our process technology and materials suit for a creation of several strongly magnetic conductive layers with different coercive fields, which can be combined with the insulating ferromagnetic layers. Thus, applications based on normal electrical conduction and tunneling are doable. The applications include devices based on the electrodes directly patterned on the insulating ferromagnetic layer, such as Bragg reflectors and waveguides. An interesting aspect is also that it is straightforward to generate desired conducting ferromagnetic patterns on an insulating ferromagnetic template, which open applications in spintronics: both planar and vertical structures are doable.

 

What we have created is a set of different types - conductive and
insulating - magnetic layers which serve as building blocks

 

The blocks can be attached with excellent interfaces, either with an abrupt composition step, or with a smooth composition gradient. We know how to process the materials so that the crystal orientation is optimized: this is in strong contrast to growth techniques in which the films are polycrystalline. An example is given here.

Processing temperatures are low and compatible with the semiconductor industry. Typical processing temperatures are between 300 and 500°C. Also few nanometers thick films can be grown. Film thickness is related to the target applications.

 

Application examples are Microwave Monolithic Integrated Circuit
(
MMIC), IC, magnetic memory cell and magnetic field sensors

 

The processing technology uses modest temperatures
compatible with the semiconductor industry requirements

 

For instance, Magnetoresistive Random Access Memory, MRAM and Spin-Transfer-Torque Magnetic Random Access Memory, STT-MRAM structures can be constructed.

Applications also benefit from an exchange bias phenomenon in which an antiferromagnet unidirectionally pins the adjacent ferromagnetic layer. The exchange bias plays a crucial role in magnetic memory devices in which the critical elements are antiferromagnetic and ferromagnetic layers. We recently demonstrated that exchange bias devices are doable by our processing technology. Processing method to control the exchange bias was developed.

 

Advanced electrode manufacturing

We provide several routes to in-situ manufacture electrodes- depending on the requirements. Structures can be grown using deposition techniques for growing dielectrics. Metallic electrodes or even entire dielectric layers can be created. Thus, no separate deposition techniques for growing metals is utilized.

 

A mask-less route for writing complex, embedded  electrode
patterns on the ATO films with high-quality lattice matching

 

The route simplifies the electrode manufacturing process and allows to make complex patterns in a fast and straightforward manner. Technique does not require masks and creates embedded electrodes, in contrast to metal electrode patterning laying on top of the film surface. Embedded structures can incorporate better electromagnetic interference protection.

 

Cost saving by in-situ electrical measurements
during electrode manufacturing

 

For example, electrode patterns of a Monolithic Microwave Integrated Circuit (MMIC) are often complex, such as meanders or a set of coplanar waveguides. This goes hand-in-hand with the high development costs associated with the designing of MMICs, which act as a major restraint for the growth of the market. MMIC design and testing is time and money consuming – significantly faster and simpler route for making MMICs is real advanced manufacturing.