Appl MOS Design

7/28/2019 Appl MOS Design

1/9

The 2DEG is located near the MgZnO/ZnO interface in a Zn-

polar ZnO substrate (sample A) or in ZnO homoepitaxial layer

(500 nm thick) (sample B).

Optical microscope image of Hall-bar devices and

measurement configurations

Insulated gate AlGaN/GaN HFET, similar to a double-

diffused metal-oxide semiconductor (DMOS) structure.

HEMT heterostructure AlGaN/GaN has been realized

by the formation of two dimensional electron gas (2DEG)via electric polarization effects, the polarization difference

between two heterojunction materials.

Like GaN, ZnO exhibits similar effect in MgZnO/ZnO

heterostructure but with several advantages over

AlGaN/GaN, including a higher saturation velocity, a lower

lattice mismatch, and the capability for bulk growth.

With increasing MgZnO thickness, the sheet resistance

reduces rapidly and then saturates. The enhancement of

the interfacial polarization effect becomes stronger,corresponding to a larger amount of resistance reduction,

when the Mg content in the cap layer increases.

AlGaN/GaN vs. MgZnO/ZnO heterostructure


2/9

Transport properties of MgZnO/ZnO heterostructure

v The electron density (n) dependence of electron mobility () for samples A and sample B at temperatures of

0.06 K, 2 K and 10 K, indicated by red, blue and black symbols, respectively.v Linear gate voltage dependence ofn for each sample.

v MgZnO/ZnO systems are therefore promising in high electron mobility transistor (HEMT) applications.


3/9

Electrical properties of modulation-doped rf-sputtered polycrystalline

MgZnO/ZnO heterostructures--- H-A Chin et al. J. Phys. D: Appl. Phys. 44 (2011) 455101

qWith 2DEG introduction by the polarization effects,

modulation doping enhances the electrical

properties in MgZnO/ZnO heterostructures of high-

quality crystals.

qThe first MgzZn1-zO thin layer is the barrier

layer, allows the carriers to transfer from the

Mgx-0.025Zn1-x-0.025O:Al0.o5 modulation doping layer to

the MgzZn1-zO/ZnO interface.

qThe second MgzZn1-zO layer is the capping layer, pins

the Fermi level of the heterostructure for higher

transferring possibility.

qBilayer heterostructure composed of a thin MgzZn1-zO

capping layer deposited on top of the ZnO thin film.


4/9

Results

When x in Mgx-0.025 Zn1-x-0.025O:Al0.025 increases, the

sheet resistance of the heterostructure decreases and

the sheet carrier density increases.

When the Mg content is raised, the band gap of MgZnO

:Al increases and the energy difference between the

donor level in the MgZnO :Al layer

Moreover, the conduction band edge of ZnO at the

MgzZn1-zO/ZnO interface becomes larger, which makes

the carriers have greater tendency to transfer from the

Mgx-0.025Zn0.975-zO:Al0.05 modulation doping layer into the

MgzZn1-zO/ZnO interface, i.e. the 2DEG region.

At a low Mg content the carrier transferring from the

modulation doping layer can significantly contribute to

the electrical conductivity and carrier concentration.

While at a high Mg content the large band gap of the

barrier layer reduces the carrier transferring probability

but the electrical properties are compensated by the

large polarization effect.


5/9

Continue

The sheet carrier density remains nearly constant

throughout the whole temperature range, indicatingthat the carrier is 2DEG and not thermally

activated.

A slight decrease in mobility at low temperatures

indicates the dominant scattering mechanism is

roughness scattering together with minor impurity

and alloy scattering

The simulation result indicates that the carrier

distribution shift towards the modulation doping layer

slightly as the Mg content in the modulation doping

layer increases.

Therefore, the slight decrease in mobility at lowtemperatures is attributed to the impurity scattering

and alloy scattering from the modulation doping layer.


6/9

Application

In recent TOYOTA hybridvehicles (HV) system, the

battery voltage is raised to

power source voltage 650V by a

voltage booster (DC-DC

converter) and then supplied to

the motor through the inverter.

The DC-DC converter and the

inverter control the electric

power over 10kW.

Si-IGBTs are used in these high power modules. Other power electronics modules

control the middle and low power, in which Si power MOSFETs are used as the power

devices.

Main problem of the high power modules is high electric power loss. On the other hand,

for the middle and low power modules, of which power level is lower than 5kW, required

breakdown voltage is lower than 600V.


7/9

Fundamental Sin-wave superimposed on PWM square wave.


8/9


9/9

Switches( S1,S2,

S3,S4) are controlled

by logic controller for

creating desired

frequency PWM wave

form.

Documents

Appl MOS Design