Capacitors, MOS

Fig. 4. Charge distributions in the voltage-biased MOS capacitor (a) accumulation of majority carriers near surface (b) depletion of majority carriers from...

The simple picture of the MOS capacitor presented in the last section is compHcated by two factors, work function differences between the metal and semiconductor and excess charge in the oxide. The difference in work functions, the energies required to remove an electron from a metal or semiconductor, is = —25 meV for an aluminum metal plate over a 50-nm thermally grown oxide on n-ty e siUcon with n = 10 cm . This work... 

Fig. 6. Electrical characterization of (a) SiGe nanocrystals (b) Ni nanocrystals embedded in HfD2 from MOS capacitors.

Figure 4.2 — (A) Schematic diagram of an ammonia-N-sensitive probe based on an Ir-MOS capacitor. (Reproduced from [20] with permission of the American Chemical Society). (B) Pneumato-amperometric flow-through cell (a) upper Plexiglas part (b) metallized Gore-Tec membrane (c) auxiliary Gore-Tec membrane (d) polyethylene spacer (e) bottom Plexiglas part (/) carrier stream inlet (g) carrier stream outlet. (C) Schematic representation of the pneumato-amperometric process. The volatile species Y in the carrier stream diffuses through the membrane pores to the porous electrode surface in the electrochemical cell and is oxidized or reduced. (Reproduced from [21] with permission of the American Chemical Society).

SiC capacitor sensors have demonstrated gas-sensitivity to gases such as hydrogen and hydrocarbons [21, 46, 68] up to a maximum temperature of 1,000°C [1, 68]. Devices that can be operated both as MOS capacitors (reverse bias) and as Schottky diodes at temperatures greater than 490°C have also been demonstrated (see Section 2.4.2) [10]. These devices showed sensitivity to combustible gases such as propane, propylene, and CO and were tested at temperatures up to 640°C. 

Schalwig et al. have tested the feasibility of using a SiC MOS capacitor sensor containing a contact metal of 40-nm TaSi plus 45-nm Pt to detect NO and HC after the catalytic converter. This was carried out by simulating lean burn engine exhausts [116]. It was observed that the sensor signal increased for NO detection and decreased for HC detection. This could permit this sensor to be used in a sensor array to differentiate these two gases. 

Agarwal, A. K., S. Seshadri, and L. B. Rolland, Temperature Dependence of Fowler-Nordheim Current in 6H- and 4H-SiC MOS Capacitors, IEEE Electron Device Letters, Vol. 18, Issue 12, December 1997, pp. 592-594. 

Sodium contamination and drift effects have traditionally been measured using static bias-temperature stress on metal-oxide-silicon (MOS) capacitors (7). This technique depends upon the perfection of the oxidized silicon interface to permit its use as a sensitive detector of charges induced in the silicon surface as a result of the density and distribution of mobile ions in the oxide above it. To measure the sodium ion barrier properties of another insulator by an analogous procedure, oxidized silicon samples would be coated with the film in question, a measured amount of sodium contamination would be placed on the surface, and a top electrode would be affixed to attempt to drift the sodium through the film with an applied dc bias voltage. Resulting inward motion of the sodium would be sensed by shifts in the MOS capacitance-voltage characteristic. 

Fig. 4. Charge distributions in the voltage-biased MOS capacitor (a) accumulation of majority carriers near surface (b) depletion of majority carriers from surface (c) inversion, accumulation of minority carriers near surface (26). VG = gate voltage Qq = gate charge xand xd = depletion widths and...

MOSFETs. The metal-oxide-semiconductor field effect transistor (MOSFET or MOS transistor) (8) is the most important device for very-large-scale integrated circuits, and it is used extensively in memories and microprocessors. MOSFETs consume little power and can be scaled down readily. The process technology for MOSFETs is typically less complex than that for bipolar devices. Figure 12 shows a three-dimensional view of an n-channel MOS (NMOS) transistor and a schematic cross section. The device can be viewed as two p-n junctions separated by a MOS capacitor that consists of a p-type semiconductor with an oxide film and a metal film on top of the oxide. 

Understanding the behavior of a MOS capacitor is useful in understanding the operation of a MOS transistor. When a negative voltage is applied to the conductor or metal, the energy bands in the p-type semiconductor... 

The operation of the NMOS transistor shown schematically in Figure 12 can be considered in the light of the previous discussion of a MOS capacitor. When no voltage is applied to the gate, the source and drain electrodes correspond to p-n junctions connected through the p region therefore only a small reverse current can flow from source to drain. On the... 

Figure 13. Energy band diagrams and charge distributions of an ideal MOS capacitor using p-type Si (a) accumulation, (b) depletion, and (c) inversion. Ef denotes the intrinsic Fermi level. (Reproduced mth permission from reference 8. Copyright 1985 Wiley.)...

Schottky-barrier diode and metal-oxide-semiconductor (MOS) capacitor gas sensors have established themselves as extremely sensitive, versatile solid state sensors. 

In contrast to r measurements, in which the decay of excess carriers is monitored the generation lifetime is determined from the reverse-biased pn junction leakage current or from the pulsed MOS capacitor (22.) latter and the more popular of the two, an MOS-C is pulsed into deep depletion and the capacitance is monitored as a function of time. An appropriate analysis of the C-t response yields t. ... 

The objective of this research work is to develop a highly conductive copper alloy based diffusion barrier for copper metallization. The criteria for selection was that minimal increase in resistivity resulted on addition of one atomic percent of second element to copper. The copper-1 at.% zinc alloy conforms to this criteria and hence was selected as a candidate material for further study. Pure copper can easily be electroplated from simple acid copper baths, but the alloys of copper are more difficult when the deposition potential of individual elements is widely separated as in the present case. A Cu-Zn alloy can be deposited from baths containing coordinating agents. Having established that a Cu-Zn alloy can be successfully electroplated, an alloy of composition Cu-3.5%Zn was sputter deposited to develop an MOS capacitor and electrical testing was performed on as-sputtered and annealed samples. The bias temperature stability tests indicate that the alloy possesses promising diffusion barrier properties. 

Fig. 6(a) and 6(b) superimpose C-V curves of the Cu-MOS and Cu-Zn-MOS capacitors respectively, in the unannealed condition, tested under no bias and BTA. In the case of copper, the C-V curves moved back and forth at increasing times of biasing. In Cu-Zn alloy, after the first movement due to annealing of surface states, the curves did not shift. 

Fig. 6 C-V Plots of as-sputtered MOS capacitors on bias temperature aging (a) Cu (b) Cu-Zn...

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