MOSFET Inversion Layer Research Articles

Physical understanding of low-field carrier mobility in silicon MOSFET inversion layer

Experimental and theoretical studies of the gate field dependencies of the low-field mobilities of electrons and holes show that by changing surface orientations and oxidation conditions the two-dimensional electron gas formulation can successfully explain eta =1/3 (where eta is the weighting factor of mobile charge density used in calculating the effective field for the universal mobility curve) for

Measurements and modeling of the n-channel MOSFET inversion layer mobility and device characteristics in the temperature range 60-300 K

Discussed is the use of the high-frequency split C-V method to measure accurately the effective mobility of the n-channel MOS transistor as a function of temperature, bulk charge Q/sub b/, and inversion layer charge Q/sub i/. The experimental data for Q/sub b/ and Q/sub i/ were verified by comparison with the results of numerical simulation. The results of the measurements were used to develop the mobility model, which is accurate in the 60-300 K temperature range. The proposed mobility model incorporates Coulombic, lattice, and surface roughness scattering modes and generalizes the previous model, which was limited to low-temperature operation of the MOSFET. The deviation from the universal (for different back biases) mu (E/sub eff/) dependence, which becomes more pronounced at low temperatures and low E/sub eff/, is included in the model and can be associated with the Coulomb scattering mechanism. The proposed model is verified by comparison of experimental data and simulated MOSFET I-V characteristics for different temperatures.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Split C-V measurements of low temperature MOSFET inversion layer mobility

A combination of the high frequency split C-V method and numerical modelling was used to accurately measure the effective mobility of electrons in the inversion layer as a function of the inversion layer change, Q i, bulk charge, Q b, and temperature. These measurements clearly show that for a sufficiently large vertical field the effective mobility is a universal function of the linear combination of Q b and Q i, E eff = ( Q b + νQ i)/ ε si for different substrate biases. The weighting factor, ν, exhibits strong temperature dependence in the 60–300 K temperature range. The results of this work suggest that the ‘effective field’ concept commonly used to model the operation of MOSFETs at room temperature can be partially extended to describe the mobility variation with the vertical field at low temperatures; however, the range of fields where the back bias does not affect the μ( E eff) dependence narrows considerably as the temperature is reduced.

MOSFET electron inversion layer mobilities - a physically based semi-empirical model for a wide temperature range

A physically based semiempirical model for electron mobilities of the MOSFET inversion layers that is valid over a large temperature range (77 K<or=T<or=370 K) is discussed. It is based on a reciprocal sum of three scattering mechanisms, i.e. phonon, Coulomb, and surface roughness scattering, and is explicitly dependent on temperature and transverse electric field. The model is more physically based than other semiempirical models, but has an equivalent number of extracted parameters. It is shown that this model compares more favorably with the experimental data than previous models. The implicit dependencies of the model parameters on oxide charge density and surface roughness are confirmed.<<ETX>>

Theory of electronic impurity states associated with primed subbands of inversion layers in silicon MOSFETs

Binding energies and transition energies for electric dipole transitions have been calculated for electronic impurity states associated with the lowest primed subbands of inversion layers of silicon MOSFETs. The results are compared with those of similar calculations for the unprimed subbands, and experimental possibilities are examined.

A semi-empirical model of the MOSFET inversion layer mobility for low-temperature operation

This paper reports on a semi-empirical model of the mobility in the inversion layer of enhancement-type MOSFET's operated at low temperatures. The n-channel model is based on three different scattering mechanisms important at cryogenic temperatures--phonon, Coulomb, and surface roughness scattering. It is shown that the degradation of the mobility with the vertical field is accelerated at low temperatures and has a different functional form compared to that at the above room temperature. The p-channel model is the extension of a high-temperature model. The simple analytical expression presented here is suitable for use in a circuit simulation program like SPICE. The definition and the temperature dependence of the effective normal field are reexamined for both n- and p-channel devices.

Comment on "A theory of enhanced impact ionization due to the gate field and mobility degradation in the inversion layer of MOSFET's"

Comment on "A theory of enhanced impact ionization due to the gate field and mobility degradation in the inversion layer of MOSFET's"

A theory of enhanced impact ionization due to the gate field and mobility degradation in the inversion layer of MOSFET's

A new explanation of carrier heating within silicon inversion layers is offered which is in full accordance with classical laws. We show that, as is usually assumed, the heating is due to the longitudinal electric field. However, also the transverse field influences the electron temperature by determining the minimum kinetic energy and therefore influencing the electron mobility. In this way the distribution function is heated above that in bulk material as witnessed by the significant increase in measured noise figures and in the calculated electron impact ionization rate.

The classical versus the quantum mechanical model of mobility degradation due to the gate field in MOSFET inversion layers

The current equation based on the classical model of mobility degradation due to the gate field fails at <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V_{GS} - V_{T}</tex> = 11, 7.5, and 4.5 V for MOSFET's with t <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">OX</inf> = 450, 350, and 250 Å, respectively, at room temperature and at very low VDS. The failure is believed to be caused by the quantization of inversion carriers in the deep potential well and the populating of the upper subbands in

Quantum effects of electrons and holes in the MOSFET inversion layer

Based on the study of mobility degradation due to the gate field, two different mechanisms of the quantum effects are proposed for inversion carriers: i) the quantization of inversion carriers and the populating of the upper sub-bands, which tend to increase the dependence of mobility on the gate field; and ii) the quantum mechanical channel broadening, which tends to decrease the dependence of mobility on the gate field. Experimental data for electrons and holes at 25 and 125°C will be reported and analyzed.

Comments on "Mobility degradation due to the gate field in the inversion layer of MOSFET's"

Comments on "Mobility degradation due to the gate field in the inversion layer of MOSFET's"

Comments on "Mobility degradation due to the gate field in the inversion layer of MOSFET's"

Fu's model [ibid., EDL-3, pp. 292-293, Oct. 1982] is based on the assumption that the thermal energy of electrons or holes in the inversion layer may be increased by the application of a gate field. In the absence of a tangential field (VDS = 0), however, carriers are in thermal equilibrium, regardless of the gate field, and hence can be characterized by a constant fermi level through the inversion layer and substrate. Indeed, as Smith (ref. [4] in Fu's paper) himself points out, the rate of increase in the thermal energy is the (dot) product of the field and the average velocity. If the average velocity is zero, there can be no heating. In fact, even in the case of an arbitrary tangential field E (VDS > 0), so large that the drift velocity is no longer simply pE, the gate field still plays no direct role in increasing the thermal energy, since it is normal to the current flowing in the channel. (To be sure it does affect the size of the current by altering the scattering rates, and hence, in this manner indirectly influences the heating of the carriers.)

Mobility degradation due to the gate field in the inversion layer of MOSFET's

A simple classical theory that explains how the carrier mobility degrades as a function of the gate field in the inversion layer of MOSFET's is presented here. A formula of effective gate field-dependent mobility is derived and is reducible to the well-known empirical formula at the limit of large gate oxide thickness. However, their difference becomes drastic at thin gate oxide and high gate fields. For example, at <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">t_{ox} = 200</tex> Å, and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V_{GS} = 5</tex> V, the difference is about 20% for mobility prediction if same physical parameters are used in both formulae. The present theory has been incorporated into a new model for <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I-V</tex> characteristics of MOSFET's and good agreements with experimental data for <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">t_{ox} = 200</tex> Å transistors have been observed.

Zeros of the transverse magneto-resistance in N-type silicon (100) inversion layers

The transverse and Hall resistance are investigated under quantizing electric and magnetic fields in n-type silicon (100) MOSFET inversion layers. The transverse resistance ρ xx vanishes within finite ranges of the gate voltage where the concentration of channel conduction electrons is constant. The variation of the oscillatory period towards low gate voltages is not compatible with the concept of carrier localization and therefore can be understood by charge transfer into states outside the surface channel.

Energy loss of warm electrons at the interface of (100) silicon MOSFETS

The electrons in inversion layers of (100) silicon MOSFETs were heated at helium temperatures with source drain fields of the order l V cm . The electron temperature as derived from the amplitudes of Shubnikov-De Haas oscillations was studied as a function of lattice temperature and substrate bias U sb . Whereas at temperatures of about 4 K. the electron temperature hardly changed with substrate bias, it increased substantially with U sb , at temperatures of 2 K and lower. This observation cannot he explained by currently discussed models for the electron energy losses. It is proposed that the low temperature behaviour arises from the anomalous thermal and dielectric properties of the amorphous SiO 2 layer adjacent to the channel. Various experiments indicate that vitreous SiO 2 can be considered as a two-level system with low energy excitations.

Absorption of ballistic phonons by the 2D electron gas in a Si mosfet

Experiments are described which measure absorption of ballistic phonons by the two-dimensional degenerate electron gas in the inversion layer of a (100)Si MOSFET; and the results are compared with theory.

Energy loss of warm electrons at the interface of (100) silicon MOSFETs

The electrons in inversion layers of (100) silicon MOSFETs were heated at helium temperatures with source drain fields of the order l Vcm. The electron temperature as derived from the amplitudes of Shubnikov-De Haas oscillations was studied as a function of lattice temperature and substrate bias Usb. Whereas at temperatures of about 4 K. the electron temperature hardly changed with substrate bias, it increased substantially with Usb, at temperatures of 2 K and lower. This observation cannot he explained by currently discussed models for the electron energy losses. It is proposed that the low temperature behaviour arises from the anomalous thermal and dielectric properties of the amorphous SiO2 layer adjacent to the channel. Various experiments indicate that vitreous SiO2 can be considered as a two-level system with low energy excitations.

ABSORPTION OF BALLISTIC PHONONS BY THE 2D ELECTRON GAS IN A Si MOSFET

Abstract Experiments are described which measure absorption of ballistic phonons by the two-dimensional degenerate electron gas in the inversion layer of a (100)Si MOSFET; and the results are compared with theory.

ENERGY LOSS OF WARM ELECTRONS AT THE INTERFACE OF (100) SILICON MOSFETs

The electrons in inversion layers of (100) silicon MOSFETs were heated at helium temperatures with source drain fields of the order 1 V/cm. The electron temperature as derived from the amplitudes of Shubnikov-de Haas oscillations was studied as a function of lattice temperature and substrate bias Usb. Whereas at temperatures of about 4 K the electron temperature hardly changed with substrate bias, it increased substantially with Usb at temperatures of 2 K and lower. This observation cannot be explained by currently discussed models for the electron energy losses. It i s proposed that the low temperature behaviour arises from the anomalous thermal- and dielectric properties of the amorphous SiO2 layer adjacent to the channel. Various experiments indicate that vitreous SiO2 can be considered as a twolevel system with low energy excitations.

Two-dimensional conductivity in the contact regions of silicon MOSFETs

The authors present evidence showing that two-dimensional conduction giving rise to Shubnikov-de Haas oscillations can occur, not only in the inversion layer of Si MOSFETs, but also in the diffused contact regions under the gate. This gives rise to additional splittings and distortion of the Shubnikov-de Haas samples when a large negative substrate bias is applied.