Passive component

Details Passive component Passive component

2001-05-30

2003-03-04

Easthom, Karl D. (Department: 2811)

Electrical resistors

With base extending along resistance element

Resistance element coated on base

C338S307000, C338S195000

Reexamination Certificate

active

06529116

ABSTRACT:

BACKGROUND OF THE INVENTION
1. The Field of the Invention
The invention relates to a passive component comprising a first track of a first material which is built up from at least a first and a second atom type and which knows a first and a second state.
2. Description of the Related Art
Such a component is known from Green et al.,
IBM Techn. Disc. Bull.
24 (1982), 5466. The known component is a resistor which has a substrate with a patterned layer of Si
72
Cr
28
, the indices indicating atom percents. The resistivity of this material is reduced by 40 to 50% through heating. A disadvantage of the known component is that the value cannot be substantially continuously adjusted over a range of at least a factor five.
SUMMARY OF THE INVENTION
It is an object of the invention to provide a passive component which has a continuously adjustable value. The object is achieved in that a first material has a first atom type and a second atom type, wherein the first material in a first state has an amorphous structure, the first material in a second state has a crystalline structure, and the second atom type is chosen from the group of gallium and germanium.
In the passive component according to the invention, the first material in the second state has a resistivity which is at least ten times, and preferably more than 1000 times lower than in the first state. In addition, the first material knows states with different structures which are each stable. A first portion of the first track is brought to at least a transition temperature through local heating, at which temperature the first material in the first portion crystallizes. Said first portion is smaller or greater in dependence on the value to which the component is to be adjusted. The value of the component is substantially continuously adjustable thereby. The value is in addition adjustable over a range equal to a factor five.
It was surprisingly found in experiments which led to the invention that the first atom type of the first material may be chosen from among various atom types, and that the second atom type may be chosen to be gallium, germanium, and indium—also referred to as Ga, Ge, and In, respectively. Preferably, the proportion of the second atom type in the first material is at least 10%. Examples of first materials are Al—Ge, Ge—Te, Ga—Sb, and In—Sb. If silicon is chosen as the second atom type, a slight drop in the resistivity was found, such as in the case of Cr—Si, or the first state is found to be not stable, such as in the case of Al—Si.
It may be that the first material comprises a third atom type. The inclusion of the third atom type in the first material renders it possible to increase the resistivity in the first state.
Heating to at least the transition temperature may be achieved inter alia by means of an electron beam, a needle-shaped heating source, a focused light beam, and a laser beam. The transition temperature generally lies between 100 and 400° C., depending on the composition of the first material. Heating is preferably performed in that the layer is locally irradiated with a laser beam. The use of a laser beam has among its advantages that dimensions of patterns can be small. Moreover, a laser beam is a known tool, and laser ablation of the first material is also possible with a laser beam.
It is a first advantage of the component according to the invention that the value of the passive component according to the invention may be adjusted also after the manufacture of the component. This is advantageous because the value of the passive component can thus be adapted to the circumstances in which the component is used.
It is a second advantage of the component according to the invention that portions of the first layer can be easily removed. Removal may take place, for example, through local heating, for example with a laser beam. The possibility of removing portions of the first layer has among its advantages that the value of the component can be restored to its original value again. As a result of this, the component may be used, for example, as a potentiometer. The removal possibility has the further advantage that, should the value have been inadvertently adjusted to a value below the desired value, this value can be corrected in upward direction again. The component would have become useless without this possibility.
It is favorable when the first atom type is aluminum and the second atom type is germanium, and the first material has a germanium content of at least 20%. The aluminum-germanium material in the second state has a dual-phase, crystalline structure; separation of the aluminum and the germanium takes place upon crystallization. It was found from experiments that the difference in resistivity between the first and the second state is very small for a germanium content of less than 20%. Examples of favorable compositions of the aluminum-germanium are shown in Table 1.
A first advantage of aluminum-germanium is that the transition temperature lies between 80 and 320° C. This is a temperature which can be easily achieved by local heating with a laser beam. At the same time, this temperature is sufficiently high for preventing a transition from the amorphous to the crystalline state under the influence of ambient factors. A second advantage of aluminum-germanium is that the ratio between the resistivity in the amorphous state and the resistivity in the crystalline state is usually more than 10
3
. A third advantage of aluminum-germanium is that the atom types aluminum and germanium are non-toxic and are accepted in clean-room conditions.
The aluminum-germanium material is known from Catalina et al.,
Thin Solid Films
167 (1988), 57-65. This article, however, does not show or suggest the use of the material in a passive component, neither as a resistor, nor as a capacitor or as an integrated passive component. The article contains no suggestion for local heating of the material.
Alternatively, the first atom type is antimony. This is also referred to as Sb hereinafter. There are various first materials with antimony as the first atom type, such as Ga—Sb and Ge—Sb—Te. The resistivity in the first state is high in these materials. In addition, the difference in resistivity between the first and the second state is satisfactory to great, i.e. from approximately a factor of 10
4
to 10
6
. The value of the component can be adjusted over a wide range by means of this difference in resistivity. It is a further advantage of antimony as the first atom type that the first material can be restored from the second state to the first state. The first material will melt when irradiated with high-intensity laser light on a small surface area. The released heat diffuses so quickly then that the first material returns to the first state. Resistivity ratios between the first, amorphous state and the second, crystalline state are given in Table 1 for various materials.
In an embodiment of the passive component according to the invention, the first track is present on a first side of a layer of dielectric material, on a second side of which an electrode is situated. The passive component in this embodiment is a capacitor with a trimmable capacitance. The first track then constitutes or forms part of a second electrode, in as far as the first material is in the second state in the first track. The second electrode may comprise a strip of electrically conducting material. A transition from the first to the second state achieved in the first track will enlarge the surface area of the second electrode, so that the capacitor will have a higher capacitance.
In a first, more specific embodiment, the first track is an interconnect between a first and a second strip of electrically conducting material. Preferably, the first and the second strip have a large surface area as compared with the first track. If the first track is in the first state, it is only the first conductive strip which forms part of the second electrode of the capacitor. An electrically conducting connection between the first and the second str

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