AHS Materials Families

AHS products versatility come from the substantial know-how, gathered by its people in the different and various aspects of thin film compound technology and device desogn and processing , and above all from the unique expertise in Molecular Beam Epiatxy (MBE), the most sophisticated thin film tool that the microelectronics industry have to day.

AHS is bringing to market "Two-dimensional electron-gas (2-DEG)" thin films, structures fabricated from III-V compounds and featuring superior properties than Silicon, GaAs, InAs or InSb Hall Effect devices and magnetoresitors. These adaptable magnetic sensors are specifically tailored by AHS to meet a range of bespoke and industrial requirements offering a choice of characteristics (see Products Data-Sheets).

AHS unique expertise in MBE grown 2-DEG structures gives it a place of choice in the market place, and no wonder that we are the only company worldwide offering this new technology and challenging more established technologies.

AHS new generation of Hall-Effect elements is based on two distinctive technologies :

Gallium Arsenide (GaAs)* and Metamorphic InGaAs (mGaAs) technologies.

The majority of AHS sensors rely, for their operation, on the concept of "Band Gap Engineering" as opposed to traditional semiconductor Hall effect sensors which rely on the "bulk" properties of the semiconductors. In other words, the physical properties of the sensors are engineered to achieve desired tasks that would simply not be feasible using natural bulk properties.

The electronic behaviours of semiconducting materials are, to a first order, governed by "bang gap" which are energy states normally forbidden to charge carrying particles such as electrons. With band gap engineering, the atomic layer precision of Molecular Beam Epitaxy (MBE) is used to deposit compound semiconductors of extremely small thickness, 10-20 nm thick ( ie 10-20 millionth of a mm). Deep inside the finished structure, potential wells are formed by growing specific combinations of materials, which constrain charge carrying electrons into fixed quantum energy state, and hence are referred to as "Quantum Wells."

AHS expertise with Band Gap Engineering and Quantum Well structures, are then translated into physical properties unavailable in traditional "bulk" or "thin film" semiconductors.

For example, a Quantum Well (QW) is built by inserting a very thin GaAs or InGaAs films between two slightly thicker, larger band gap semiconductors (such as AlGaAs or InAlAs) giving rise to the Quantum Well concept (see Figure 1). This QW is then able to "trap" electrons which are then called a 2 Dimensional Electron Gas (2DEG), so called because they are trapped within the QW plane, in effect confining them to 2 dimensions instead of being free to "roam" the semiconductor crystal in 3D as is the case for conventional Hall effect sensors.

Figure 1 Quantum Wall Structure

The generic structure of the QW Hall effect sensors manufactured by AHS is depicted below:

Generic Hall Effect Structure

Each component of the Hall sensor is optimised with the view to performing over a very large range of temperature and magnetic fields. The control over the material systems and over the thickness of the QW and its associated 2DEG permits control over the Magnetic Sensitivities, ranging from 180 — 1000 V/AT (2 to 5 times existing commercially available GaAs, InAs, or InSb Hall sensors with very low thermal drifts ( < -0.05% oC) and magnetic non-linearity (<1%).

The new 2-DEG Hall-Effect elements have outstanding performances, and extraordinarily controlable parameters at the material level, featuring:

variable and reaching sensitivies higher than traditional InSb. It is a controlable parameter at the material level (wafer growth) (Far more superior to the optimal use of the sensitivity of the InSb MR elements when the magnetic field B is on the order of 0.2 to 0.4 T).

Excellent temperature stability — extremely low drift
Controlable and predictable temperature coefficient.
(amplification versus magnetic field).

No Piezo-electric effect
Commercial Hall-effect elements respond to stress by modifying the Output voltage vs. the magnetic flux-density curve. For this reason, environmental stress from hot, cold, or mechanical sources affect the output of commercial Hall-effect elements. AHS elements do not suffer from this effect, and hence do not require any special handling care.

Very high bandwidth
Operations up to several MHz.

Offset Voltage
Very low offsets as a consequence of the high mobilities of the 2DEG structures.