The AHS Manufacturing Process
AHS utilises Molecular Beam Epitaxy techniques to manufacture thin film wafers, which are subsequently processed into Hall Sensor devices. There are three distinct stages to the device production process.
Stage 1: Thin films of compound semiconductor compounds such as Gallium Arsenide , Indium Gallium Arsenide or Indium Arsenide are deposited onto substrates using the technique of Molecular Beam Epitaxy to form wafers containing two dimensional electron gas thin film structures.
Stage 2: The wafers are processed into Hall sensors. This processing is done in a clean room environment, involving process steps such as lithography, etching, annealing and metal evaporation. The Hall sensors are tested and the wafer cut into individual devices.
Stage 3: The Hall sensors are then packaged (either into a surface mount IC package such as SOT 143 or a SLOT E-line package) and final product testing.
AHS products' superior performance and versatility come from the business's unique expertise in Molecular Beam Epitaxy and in the optimisation of the wafer processing steps.
The use of Molecular Beam Epitaxy at AHS enables "band gap engineering" to be utilised. "Band Gap Engineering" involves growing specific combinations of materials deep inside the finished structure of the wafer. These materials (of the order of 10-20 nanometers thick) constrain charge-carrying electrons into a fixed quantum energy state – known as a "Quantum Well".
AHS generates its Quantum Wells by inserting a very thin GaAs or InGaAs film between two slightly thicker, larger band gap semiconductors (such as AlGaAs or InAlAs) – see Figure 2 below. This Quantum Well is then able to "trap" electrons - referred to as 2 Dimensional Electron Gas (2DEG) - within the Quantum Well 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 2: Quantum Well Structure
This process of band gap engineering alters and improves the electronic behaviours of semi conducting materials and hence produces sensors with physical properties that are not feasible in traditional "bulk" or "thin film" semiconductors.