Active solid-state devices (e.g. – transistors – solid-state diode – Field effect device – Having insulated electrode
Reexamination Certificate
1999-05-07
2002-11-12
Chaudhuri, Olik (Department: 2814)
Active solid-state devices (e.g., transistors, solid-state diode
Field effect device
Having insulated electrode
C257S410000, C438S003000
Reexamination Certificate
active
06479847
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to integrated circuits and, more specifically to a complementary transistor structure having a Mott material oxide channels.
2. Description of the Related Art
Silicon based metal oxide semiconductor field effect transistors (MOSFETs) are reaching the limits of scaling (e.g., reduction in size) due to, among other things, doping and double depletion effects. In other words, as semiconductor devices are reduced in size, the depletion regions are placed in closer proximity to one another. This often results in merging or shorting of the adjacent depletion regions.
Silicon MOSFET technology is expected to scale to 0.1 micron channel length devices after the year 2000. Below 0.1 microns however, there are fundamental physical effects which can limit silicon MOSFET technology, including: short channel effects, dopant number fluctuations, ballistic transport and tunneling through thin gate oxides. These effects may limit the minimum channel length in silicon MOSFET technology to an estimated 30 nm.
One solution to the scaling problem is a field effect transistor (FET) formed with a channel oxide capable of undergoing a metal-insulator transition known as a Mott transition (e.g., a Mott FET or MTFET).
A Mott FET is a solid state switching device made of oxide materials and is discussed in more detailed in Mott Transition Field Effect Transistor, Applied Physics Letters, Vol 73, Number 6, pages 780-782, Aug. 10, 1998, incorporated herein by reference. The Mott FET device includes a channel connecting source and drain electrodes, a gate oxide and a gate electrode.
For example, a Mott FET device is shown in FIG.
13
. The device includes a conductive substrate
1301
(e.g., Nb-STO (100)-cut crystal) which forms the gate electrode, a gate oxide layer
1300
(e.g., strontium titanate (STO)) epitaxially grown on the substrate
1301
, a Mott conductor-insulator transition channel
1302
(e.g., epitaxially grown cuprate material such as Y
1−x
Pr
x
Ba
2
CU
3
O
7−&dgr;
(YPBCO, LCO)), source and drain electrodes
1303
and an isolation trench
1304
. With the structure shown in
FIG. 13
, when an electric field is applied to the gate
1300
, the channel
1302
changes from an insulator to a conductor (or vice versa) to make or break a connection between the source and drain
1303
.
The Mott FET device is quite distinct from conventional silicon metal oxide field effect transistors in that the channel is a Mott insulator, a material with a characteristic, controllable, conductor-insulator transition, used in place of a semiconductor. A Mott FET device offers significant potential for scaling to the nanometer dimensions for integration with ferroelectric materials in non-volatile storage roles and for fabrication of multilayer device structures. Mott FET devices remain adequate on a nanoscopic scale which is well beyond the current projected limits of silicon MOSFET scaling.
However, the Mott FET discussed above has a number of limitations. Specifically, the structure shown in
FIG. 13
results in the channel layer
1302
being exposed to subsequent processing steps, which may damage or undesirably change the channel layer
1302
. Also, conventional Mott-FET devices suffer from the shortcoming that the channel layer is not protected. Further, they have a common gate electrode which does not allow the formation of a complementary cell.
SUMMARY OF THE INVENTION
It is, therefore, an object of the present invention to provide a structure and method for manufacturing a complementary field effect transistor structure that includes forming a first type Mott channel layer and forming a second type Mott channel layer adjacent the first type Mott channel layer, wherein the first type Mott channel layer is complementary to the second type Mott channel layer.
The method may also include forming a first source region, a first drain region and a first gate conductor region adjacent the first type Mott channel layer and forming a second source region, a second drain region and a second gate conductor region adjacent the second type Mott channel layer. The first source region, the first drain region, the first gate conductor region and the first Mott channel layer are a first type field effect transistor and the second source region, the second drain region, the second gate conductor region and the second type Mott channel layer are a second type field effect transistor electrically connected to the first type field effect transistor.
The forming of the first source region and the first drain region includes forming a first conductive layer adjacent the first type Mott channel layer and forming a first insulator region in the first conductive layer opposite the first gate conductor. The first source region and the first drain region are regions in the first conductive layer on opposite sides of the first insulator region.
Similarly, the forming of the second source region and the second drain region includes forming a second conductive layer adjacent the second type Mott channel layer and forming a second insulator region in the second conductive layer opposite the second gate conductor. The second source region and the second drain region are regions in the second conductive layer on opposite sides of the second insulator region.
Also, the forming of the first gate conductor region and the forming of the second gate conductor region include forming a gate conductor layer insulated from and positioned between the first type Mott channel layer and the second type Mott channel layer (the first conductive layer and the second conductive layer respectively being on opposite sides of the first type Mott channel layer and the second type Mott channel layer from the gate conductor layer) and forming a plurality of insulator regions in the gate conductor layer. The first gate conductor region is a region of the gate conductor layer between two of the insulator regions and is positioned opposite and between the first source region and the first drain region. Similarly, the second gate conductor region is a region of the gate conductor layer between two of the insulator regions and is positioned opposite and between the second source region and the second drain region.
The method may also include forming a first conductive oxide layer as the first conductive layer, forming the first type Mott transition layer on the first conductive oxide layer, forming a first gate insulator layer on the first type Mott channel layer, forming a second conductive oxide layer as the gate conductor layer on the first gate insulator layer, forming a second gate insulator layer on the second conductive oxide layer, forming the second type Mott channel layer on the second gate insulator layer and forming a third conductive oxide layer as the second conductive layer on the second type Mott channel layer.
The first type Mott channel layer and the second type Mott channel layer change conductivity in the presence of an electric field. The first type field effect transistor and the second type field effect transistor can be connected to form a complementary field effect transistor.
Another inventive method of manufacturing a complementary field effect transistor structure includes forming a laminated structure having a first side and a second side (the first side including a first type Mott channel layer and the second side including a second type Mott channel layer), forming a first source region and a first drain region in a first conductive layer on the first side, forming a second source region and a second drain region in a second conductive layer on the second side and forming a first gate conductor region and a second gate conductor region in a gate conductor layer positioned between and insulated from the first type Mott channel layer and the second type Mott channel layer. The first source region, the first drain region, the first gate conductor region and the first type Mott channel layer make a first type field effect transistor and
Misewich James A.
Schrott Alejandro G.
Scott Bruce A.
Rao Shrinivas H.
Underweiser, Esq. Marian
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