Transistors

The structure of the metal-insulator diode may be extended to form a tunneling transistor that provides signal gain at extremely high frequency (Figure 1).

Phiar's tunneling hot electron transistor structure.

Half of the transistor functions much like a diode. A voltage applied between the emitter and base metal layers induces an electron tunneling current that traverses the insulator separating them. In the transistor, however, the base metal layer is so thin that most of the ballistic electrons are not stopped in the base layer. They continue through to the collector. In this way the emitter-base voltage determines the emitter-collector current.

For a metal-insulator transistor to work well, the emitter must produce electrons that have a precisely controlled energy distribution. The red lines are simulated data which illustrate the tighter distribution achieved in an MIIMIM design vs. MIMIM.

A significant problem with MIMIM transistors has to do with injected electrons successfully traversing the collector electrode (Figure 2). The probability of hot electrons scattering in the base metal increases with increasing electron energy, but electrons having too low an energy will be clipped by the barrier at the oxide between the base and collector. With a single-insulator MIMIM transistor there is a substantial spread in the energies of the injected electrons, as shown in the figure, and so the scattering in the base and clipping by the collector oxide is a real problem. On the other hand, with a double-insulator MIIMIM transistor the injected electrons have a much narrower range of energies, as shown in the figure. This nearly mono-energetic stream of electrons largely avoids the scattering and clipping losses. This translates into higher overall performance of the transistor.

Phiar's technology stacks up nicely against other high performance options. This chat shows projected 2010 performance figures. Phiar aims to deliver unprecedented speed in its transistors, while keeping manufacturing costs close to those of CMOS devices.

Simulations show that the MIIMIM transistor can outperform any other available technology (Figure 3). Not only will it operate at higher frequencies than compound semiconductor devices, but it will do so at with a lower cost, more easily integrated technology.

Why is the MIIMIM transistor so fast? The speed is due to the extremely short transit time for the electrons, and to the reduced base and lead resistance as compared to semiconductor devices.