Semiconductor device manufacturing: process – Making regenerative-type switching device
Reexamination Certificate
2000-05-25
2002-09-03
Mulpuri, Savitri (Department: 2812)
Semiconductor device manufacturing: process
Making regenerative-type switching device
C361S321600
Reexamination Certificate
active
06444504
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention belongs to field of electronic components and more specifically into multifunctional and/or multipurpose electronic elements. Such elements provide simultaneous and independent exploitation of several electric properties, which are result of activity of various physical mechanisms, in common material structure. Even more narrow definition places this invention in the field of polycrystalline semiconductor diodes.
Diode of this invention differs from standard planar monocrystalline Si based diodes, as it provides higher capacitance with stable temperature and wide range of frequency properties, which enables the diode to perform condenser function. Capacitance of this newly disclosed diode may be controllable altered, by the means of voltage, which provides similar function as known for varactor diodes (word varactor is developed from variable reactor).
I—U characteristic of the subject diode is not linear and a pulse mode breakthrough is not destructive, which provides similar function as known for Zener protective diodes.
BRIEF SUMMARY OF THE INVENTION
A method of manufacturing a multilayer ZnO polycrystalline diode that protects against electrostatic discharges, over-current, and voltage surges overcoming the aforementioned drawbacks is provided. The present invention further includes preparing a plurality of oxide additives and homogenizing the oxide additives with ZnO. A plurality of polycrystalline layers is then formed having a thickness of approximately 20 to 60 microns. The method further includes forming a plurality of polycrystalline layers, each having a thickness of approximately 20 to 60 microns, printing an inner electrode on each polycrystalline layer, forming a compact block with the polycrystalline layers, cutting the compact block into a plurality of chips, scorching and sintering the plurality of chips, forming a plurality of outer electrodes, scorching the outer electrodes, and placing at least two of the outer electrodes on each chip.
There are four basic problems, from aspects of use of planar Silicon (Si) diodes as protective elements:
1. In voltage range v<4V Si diodes have high leakage current (reverse current) and high negative breakthrough coefficient, which excludes Si diodes from above voltage range, as protective elements.
2. Energy absorption capability of Si protective diodes, at higher voltage, is very limited. This is due the planar construction and small volume of reduced P—N area, where all absorbed energy is concentrated, respectively. Any increase of absorption capability of diodes automatically claims increase of their dimensions, and as result price, which is not in accordance to demands of contemporary electronic and microelectronic.
3. In many various applications, especially when voltage stroke and frequency disturbance appear simultaneous, the protective element shall have capacitance as high as possible. The capacitance of Si Zener diodes is usually small therefore normally condenser is parallely added.
4. Use of Si planar diodes as SMD elements, due their construction, demands mounting in special plastic housings, which additionally increases their dimensions and price.
Technical problem solved with this invention arises from special and general demands of electronics for contemporary protective components.
a) Special Demands
1. Widest possible operating voltage rang of diode
2. Non-destructive and temperature independent breakthrough
3. Relatively high capacitance, stable in wide temperature and frequency range
4. Controllable change of capacitance by means of voltage in whole range of operating voltage
b) General Demands
1. Ilimitability of small and large dimensions
2. Choice and change of electrical parameters in wide range
3. Possibility of surface mounting
P—N junction and potential barrier on it respectively represents base of functioning of the most elementary active semiconductor two terminal component diode. The most commonly used material for manufacturing semiconductor diodes is silicon monocrystalline. Selective and controlled forming of N, N+ type areas respectively, and P, P+ type respectively is achieved with diffusion or ionic implantation in such manner that the most of formed P—N junction is located in monocrystaline depth, where the surface remains even, thus planar (planar technology). Depending on doping profile, geometry, and polarization conditions, diode offers various useful functions for different types of applications.
Breakthrough I—V characteristic of planar diodes is very non-linear, which provides use of diodes as protective elements against electrostatic discharge and voltage strokes. Namely, at lower voltages, through diode current is very low however, when electric field on P—N junction reaches certain value (about 10
6
V/cm) diode resistance rapidly decreases and very high current runs through the diode. Such diode behaviour is caused by two different mechanisms: a) tunnel effect; and b) avalanche like multiplication, where the value of breakthrough voltage mostly depends on width of reduced area and dope level respectively of N and P area. Both mechanisms are often very actively used in various fields of application, one of the fields being protection.
Tunnel effect is known for Si diodes, with breakthrough voltage vp,4E
g
/q (E
g
-semiconductor suppressed band energy, q-elementary charge). As E
g
with increasing temperature decreases, such diodes have expressly negative temperature coefficient. Further more, leakage current of such diodes in breakthrough area is very high, which disables them to function as protective elements, especially at DC electronic circuits. If breakthrough voltage Vp>6E
g
/q than avalanche like multiplication is basic breakthrough mechanism. In such case breakthrough voltage is positive and breakthrough voltage is increasing with temperature. If diode breakthrough voltage 4E
g
/q<Vp<6E
g
/q, both breakthrough mechanisms function at the same time.
Regardless to the fact that capacitance, as result of reduced area of P—N junction, is one of its basic features, diodes are exceptionally used as condenser, however mostly in special cases. This is due to low dielectric constant of silicon (&egr;=11.9), low value of surface capacitance (<10 nF/cm2) and due to limits of planar technology, which are also related to price.
Wideness and capacitance of reduced area is directly related to its voltage. This is utilised in varactor diode, where capacitance may be controllable altered with voltage. Because of these properties varactor diodes are widely used in parameter boosters, harmonisation generators, signal mixing systems, detectors and as voltage altered trimmers for precise setting of resonance frequency. Beside high sensitivity (s>3) of temporary varactor diodes with hyper gradient junction in some applications they show deficiency, e.g. relatively low value of nominal capacitance, large dimensions and incapacity of surface mounting. It is obvious that possibilities of planar Si technology are limited, when all demands of contemporary protective electronic components must be fulfilled. This is especially case when necessary for the component to have the highest possible capacitance (e.g. frequency disturbance filtration) or when very high and frequent energy loads are present (electricity in automobiles).
Some of above mentioned problems could be solved using new materials and structures. European patent EP 41 8394A of Matsushita Company, introduced multilayer condenser based on SrTiO
3
semiconductor, which has varistor characteristic. Because of high value of &egr; (i.e.>15000), such condenser provides very high capacity, varistor function being worse side of this product. Namely in prebreakthrough area varistor characteristic has high leakage current, thus highest operating DC value must 50% lower, compared to varistor breakthrough. Further more non-linearity coefficient a does not exceed value 15, which makes efficiency of the protection very limited. U.S. Pat. No. 4,811,164 introduces conden
LandOfFree
Multilayer ZnO polycrystallin diode does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Multilayer ZnO polycrystallin diode, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Multilayer ZnO polycrystallin diode will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2823635