Tutorial 4 tasks and submission

Task 1

Explain the importance of this device for an application perspective. What color (or spectral range) does it emit?

Extra: Can you name the fabrication process for these layers and any potential issues with the complicated multi-layer stack?

Task 2

An nMOSFET has 1 nm SiO₂ as gate oxide and a doping concentration
N_a=10¹⁷ cm^-3 in the body.
Estimate the threshold voltage V_T. Use a typical work-function value for the compound TiN and refer to 5-8 in the course book.

Find data for TiN in this article that is available within the KTH network (VPN).
http://ieeexplore.ieee.org/stamp/stamp.jsp?arnumber=4011932 Links to an external site.

Task 3

The flat-band condition is useful to analyze the MOS-system. Draw the energy band-diagram for a MOS-system in flat-band condition using the following information:

• p-type substrate
• n⁺ poly-silicon gate
• a positive charge located at the oxide-substrate interface

Hint: you could start from the normal flat-band condition with no surface charge and then add the influence of the positive charge. Also refer to relevant parts of the book.

Task 4

An nMOSFET has a dual layer of 1 nm SiO₂ (closest to the silicon surface) and 3 nm HfO₂ (on top) as gate dielectric stack, to prevent severe leakage. Sketch the voltage distribution in this system, for a flatband condition, assume n-type polysilicon gate and p-type substrate. Assume that HfO₂ has a band gap of roughly 6 eV, and electron affinity of 2.14 eV, and e_r=16

Extra: can you figure out an effective oxide thickness normalized to the SiO₂ dielectric constant for this dual layer stack?