Molecule-doped negative-resistance device and method for manufacturing the same

There is provided a negative-resistance device which is easier to manufacture and can be manufactured at a lower cost as compared with the prior art, and yet has a comparatively large PV ratio, and a method for manufacturing the same. The negative-resistance device is a molecular-doped negative-resistance device which comprises a molecular-doped layer (2) made of an electron transporting lower molecular organic compound, in which the molecular-doped layer (2) is formed to be sandwiched between a pair of electrodes (2, 4), in which respective molecules of said electron transporting lower molecular organic compound are isolated from one another by an electrically insulating organic polymer, and in which said molecular-doped negative-resistance device has a negative-resistance. By doping the lower molecular organic compound in the electrically insulating organic polymer, the molecular-doped layer (3) has a multiple barrier type molecular doping structure, such that contacts each between the organic polymer and a molecule of the lower molecular organic compound are repeated in an alternate order of the organic polymer and the molecule of the lower molecular organic compound. The lower molecular organic compound is preferably a triphenyldiamine derivative or 8-hydroxy-quinoline aluminum, and the organic polymer is poly (N-vinylcarbazole) or polystyrene.

TECHNICAL FIELD 
The present invention relates to molecular-doped negative-resistance 
devices having a negative-resistance and switching and rectifying 
characteristics, in the field of organic molecular electronics, and a 
method for manufacturing the same. More particularly, the present 
invention relates to a molecular-doped negative-resistance device having a 
negative-resistance which is fabricated by using an electrically 
insulating organic polymer and a lower molecular organic compound, and a 
method for manufacturing the same. 
BACKGROUND ART 
Conventionally, as a negative-resistance device, there have been proposed 
various super lattice elements including those formed from single crystals 
of inorganic materials such as GaAs, AlAs and the like, and those formed 
from a combination of a single crystal of inorganic material and an 
inorganic amorphous material or electrically insulating organic polymer. 
Most of these are such that a thin film is formed by the molecular beam 
epitaxy technique (hereinafter referred to as an MBE process). This 
requires treatment under extremely severe conditions, such as ultra-high 
vacuum, high temperature conditions and the like and the use of a very 
costly and large-sized film forming apparatus. The process also requires 
strict control, and this makes it difficult to manufacture such a device 
uniform over a wide area. Further, semiconductors available for use are 
limited. 
In the Japanese Patent Application Laid-Open Publication No. 6-29556, there 
is proposed a resonant tunneling diode having a negative-resistance 
characteristic which includes a fullerene thin film formed from a carbon 
cluster as an organic material and an electrically insulating thin film in 
which is used a metal oxide, the thin films being sandwiched between 
electrodes. This publication points out or suggests that an electrically 
insulating organic compound and an electrically insulating organic polymer 
matrix can be used as an electrically insulating layer. However, it is 
difficult to form an electrically insulating layer to the thickness of 3 
to 15 nm, a thickness required for obtaining negative-resistance 
characteristics. In the publication, no example is shown of a tunnel diode 
in which the electrically insulating layer is formed from such 
electrically insulating organic materials. 
Recently, an electroluminescence device having a quantum well structure 
formed by vacuum vapor depositing ultra-thin films of organic dyes 
alternately by an organic molecular beam evaporation method has been 
proposed in, for example, the prior art literature 1, Hiroshi Ohmori, et 
al, "Organic Quantum Well Structure EL Device", Monthly publication of The 
Japan Society of Applied Physics, Vol. 64, No. 3, pp. 246-249, 1995. 
However, the device has not demonstrated any negative-resistance 
characteristic. 
In an operation at a room temperature, a negative-resistance device is 
required to exhibit a large ratio of peak current to valley current (the 
term "ratio of peak current to valley current" is hereinafter referred to 
as a "PV ratio"). However, the PV ratio of a resonant tunnel diode in 
which GaAs is used is about 7.7 at a temperature of 77 K (See, for 
example, prior art literature 2, Takayuki Nakagawa, et al, "Effect of 
Prewell Insertion in InGaAs/A1As/InAs resonant tunneling diodes", Papers 
at Autumn General Meeting, 1995 of the Japan Society of Applied Physics 
Society, 29a-Zm-8, 1995). 
On a junction interface of a negative-resistance device using an inorganic 
single crystal there exists a non-joinable surface level arising from 
dangling bonds which is characteristic of crystals. Development of such a 
surface level and degradation of crystallinity on the junction interface 
leads to lowering the interface electric field, thus lowering the 
efficiency of carrier injection with the result that the 
resonant-tunneling effect of the device is substantially affected. 
A device comprising a combination of an electrically insulating organic 
polymer and an inorganic single crystal is inevitably thermally unstable 
and physically fragile because the thermal expansion coefficient of 
organic material is larger than that of inorganic material by about an 
order of magnitude. Inorganic single crystal materials are only available 
in limited kinds, i.e., GaAs and Si, and therefore negative-resistance 
devices using such materials permit only a lower freedom of material 
selection. Further, the prior art layer structure which comprises 
alternately stacked crystals of different compositions is complex in 
construction and is less processable. The MBE process which has hitherto 
been largely employed upon manufacturing the negative-resistance devices 
is such that crystal growth of component elements is carried out in 
ultra-high vacuum and under strict control. This poses the problem of 
lower productivity. Another problem is that the process requires a very 
costly film forming apparatus. 
An object of the present invention is to provide a negative-resistance 
device which solves the above-mentioned problems, is easier to 
manufacture, can be manufactured at lower cost as compared with the prior 
art device, and yet has a comparatively large PV ratio, and a method for 
manufacturing the device. 
DISCLOSURE OF THE INVENTION 
A molecular-doped negative-resistance device according to the present 
invention comprises: 
a molecular-doped layer made of an electron or hole transporting lower 
molecular organic compound, said molecular-doped layer being formed to be 
sandwiched between a pair of electrodes, 
wherein respective molecules of said electron or hole transporting lower 
molecular organic compound are isolated from one another by an 
electrically insulating organic polymer, 
wherein said molecular-doped negative-resistance device has a 
negative-resistance. 
In the molecular-doped negative-resistance device, the molecular-doped 
layer has a multiple barrier type molecular doping structure, such that 
contacts each between the organic polymer and a molecule of the lower 
molecular organic compound are repeated in an alternate order of the 
organic polymer and the molecule of the lower molecular organic compound, 
by doping the lower molecular organic compound in the electrically 
insulating organic polymer. 
Further, in the molecular-doped negative-resistance device, preferably the 
lower molecular organic compound is a triphenyldiamine derivative or 
8-hydroxy-quinoline aluminum, and wherein the organic polymer is poly 
(N-vinylcarbazole) or polystyrene. 
A method for manufacturing a molecular-doped negative-resistance device 
according to the present invention includes the following steps of: 
forming a first electrode on a substrate; 
doping an electronic carrier transporting lower molecular organic compound 
into an electrically insulating organic polymer, thereby forming a 
negative-resistance material having a multiple barrier type molecular 
doping structure such that contacts each between the organic polymer and a 
molecule of the lower molecular organic compound are repeated in an 
alternate order of the organic polymer and the molecule of the lower 
molecular organic compound; 
forming a molecular-doped layer by forming said formed negative-resistance 
material on the first electrode using a dip coating method or spin coating 
method; and 
forming a second electrode on the molecular-doped layer. 
In the method for manufacturing the molecular-doped negative-resistance 
device, the lower molecular organic compound is preferably a 
triphenyldiamine derivative or 8-hydroxy-quinoline aluminum, and the 
organic polymer is poly (N-vinylcarbazole) or polystyrene.

BEST MODE FOR CARRYING OUT THE INVENTION 
Preferred embodiments according to the present invention will now be 
described with reference to the accompanying drawings. 
In order to thoroughly eliminate the foregoing deficiencies of the prior 
art negative-resistance devices, the inventor examined negative-resistance 
devices in which functions of organic molecules were utilized, that is, 
so-called molecular devices. As a result, it was found that, by doping a 
charge transferring lower molecular organic compound having a short 
molecular length into an electrically insulating organic polymer, there is 
formed a molecular doping structure comprising: 
an electrically insulating organic polymer serving as a potential barrier; 
and 
a lower molecular organic compound having the lowest unoccupied level 
(hereinafter referred to as an LUMO) and the highest occupied level 
(hereinafter referred to as a HOMO), and 
that a device with the molecular doping structure formed to be sandwiched 
between two electrodes would exhibit negative-resistance characteristics. 
This led to he development of the present invention. 
FIG. 1 is a plan view showing a configuration of a molecular-doped 
negative-resistance device according to a preferred embodiment of the 
present invention. FIG. 2 is a sectional view along the line A-A' which 
shows a construction of the molecular-doped resistance device shown in 
FIG. 1. The molecular-doped negative-resistance device embodying the 
present invention is manufactured in manner as described below. 
As shown in FIG. 1, first of all, a first electrode or anode 2 is formed on 
a substrate 1 made of an electrically insulating substrate such as a glass 
substrate or the like, then an electronic carrier transporting lower 
molecular organic compound is doped into an electrically insulating 
organic polymer, this leads to that a negative-resistance material is 
formed which has a multiple barrier type molecular doping structure such 
that contacts each between the organic polymer and a molecule of the lower 
molecular organic compound are repeated in an alternate order of the 
organic polymer and the molecule of the lower molecular organic compound. 
Thereafter, the so formed negative-resistance material is coated on the 
anode 2 using the dip coating method or the spin coating method to thereby 
form a molecular-doped layer 3. Then, a second electrode or cathode 4 is 
formed on the molecular-doped layer 3. The positive pole of a bias DC 
power supply 10 is connected to the anode 2, while on the other hand the 
negative pole of the bias DC power supply 10 is connected to the cathode 
4. 
Thus, the molecular-doped negative-resistance device is formed which 
comprises a molecular-doped layer 3 such that a single molecule of a hole 
transporting or electron transporting lower molecular organic compound and 
an electrically insulating organic polymer are alternately repeated, the 
molecular-doped layer being formed so as to be sandwiched between two 
electrodes, i.e., the anode 2 and the cathode 4, in which the device has a 
negative-resistance. The molecular-doped layer 3 has a multiple barrier 
type molecular doping structure such that the lower molecular organic 
compound is doped in the electrically insulating organic polymer such that 
contacts each between the organic polymer and a molecule of the lower 
molecular organic compound are repeated in an alternate order of the 
organic polymer and the molecule of the lower molecular organic compound. 
In a preferred embodiment, the lower molecular organic compound is 
preferably a triphenyldiamine derivative (hereinafter referred to as TPD) 
or 8-hydroxy-quinoline aluminum (hereinafter referred to as Alq.sub.3), 
and the organic polymer is preferably poly (N-vinylcarbazole) hereinafter 
referred to as a PVCZ) or polystyrene hereinafter referred to as a PS). 
Therefore, the molecular-doped negative-resistance device embodying the 
present invention, unlike he conventional device of the kind, has a 
multiple barrier type molecular doping structure such that individual 
carrier-transporting molecules are isolated from one another by an 
electrically insulating material having a several nm order. The molecular 
doping structure is formed by doping the hole transporting or electron 
transporting lower molecular organic compound, such as triphenyldiamine 
derivative (TPD), 8-hydroxy-quinoline aluminum (Alq.sub.3) or the like, 
into a polymer matrix, that is, an electrically insulating organic 
polymer, such as poly (N-vinylcarbazole) (PVCz), polystyrene (PS), or the 
like, and the intermolecular distance in the lower molecular organic 
compound is changed by changing the dopant concentration. The structure 
can be a super lattice structure depending upon the manner of arrangement 
of molecules of the lower molecular organic compound. A polymer thin film 
having such lower molecular organic compound doped therein (hereinafter 
referred to as molecular-doped polymer thin film, which expression is 
generalized so that a B thin film having A doped therein is called 
"A-doped B thin film") is formed so as to be sandwiched between a metal of 
the anode 2 having a large work function and a metal of a cathode having a 
small work function or the cathode 4 having a large work function. This 
results in formation of the molecular- doped negative-resistance device 
having a negative-resistance. 
The molecular-doped polymer thin film of the molecular-doped layer 3 is 
formed on a vacuum vapor deposited anode substrate using the dip coating 
method or the spin coating method, with a dispersion liquid formed such 
that the electronic carrier transporting lower molecular organic compound 
and the electrically insulating organic polymer material are dissolved in 
an organic solvent. Then the organic polymer thin film in which the lower 
molecular organic compound is doped is formed between the metal of the 
anode 2 having a large work function, such as ITO, Au or the like, and the 
metal of the cathode 4 having a small work function, such as Mg, Al or the 
like. Thus, the molecular-doped negative-resistance device of a 
negative-resistance tunneling device is obtained. 
The molecular-doped resistance device of the preferred embodiment is 
different from the conventional resonant tunneling diodes in that the 
negative-resistance thereof is obtained by virtue of the tunnel effect at 
the interface between the electrode metal and the lower molecular organic 
compound and of the phenomenon of polarization as developed by electrons 
trapped in lower molecular LUMO or holes trapped in HOMO. A hole that is 
tunnel-injected from the anode 2 into HOMO of the lower molecular organic 
compound tunnel-electrically-conducts across the lower molecular organic 
compounds doped in the organic polymer. That is, when the hole injected 
from the anode 2 is trapped in a lower molecular HOMO, the hole polarizes 
the surroundings with its electric field. The hole-trapped HOMO 
(hereinafter referred to as an occupied HOMO) loses the energy due to the 
polarization and its energy level is lowered. On the other hand, when a 
HOMO adjacent to an occupied HOMO (hereinafter referred to as an empty 
HOMO) is made to have the same level as that of the occupied HOMO by an 
external electric field, the hole tunnels the electrically insulating 
polymer between lower molecules. As the external electric field increases, 
an empty HOMO adjacent to an electrode interface gets close to the Fermi 
level of the electrode metal, and when an occupied HOMO in the bulk 
approaches the level of the empty HOMO, there occurs a current increase. 
When the occupied HOMO goes away from that level, the current decreases. 
Thus, a so-called negative-resistance is produced. Where the electron 
transporting organic compound is doped in the electrically insulating 
organic polymer, an electron tunnel-injected from the cathode 4 
tunnel-electrically-conducts across the lower molecular organic compound 
dope. The electronic carrier that passes through the electrically 
insulating polymer to electrically conduct across the doped lower 
molecular organic compounds may be an electron or hole. It is noted in 
this connection that the process of tunnel-injecting the hole and electron 
from the anode 2 or the cathode 4 is not dependent upon the temperature. 
However, the potential barrier is dependent upon the energy level 
difference between the electrode material and the lower molecular organic 
compound. 
The electrically insulating organic polymer used in the molecular-doped 
negative-resistance device of the present preferred embodiment may be any 
such material as PVCz or PS which is soluble in an organic solvent such as 
chloroform, 2-dichloroethane or the like. On the other hand, for the lower 
molecular organic compound, any hole transporting or electron transporting 
material, such as TPD, Alq.sub.3 or the like, which has a molecular length 
of an order of 2 nm may be used as long as it is soluble in organic 
solvents. The concentration of the molecular doping or dispersion is 
preferably so determined as to give an average distance between molecules 
of the order of 2 nm. There are many kinds of organic materials usable in 
the molecular-doped negative-resistance device of the present preferred 
embodiment, and this affords great freedom of material selection. In fact, 
however, in order to obtain a satisfactory combination of an electrically 
insulating organic polymer and a carrier transporting lower molecular 
organic compound, it is necessary to prepare energy band diagrams for 
respective materials. 
In order to obtain a greater PV ratio, any thermal current component 
resulting from other than tunneling should be decreased. For this purpose, 
a material combination is selected which can produce a larger difference 
in the HOMO or the LUMO between the electrically insulating organic 
polymer and the carrier transporting lower molecular organic compound to 
thereby provide an increased potential barrier height. In this case, it 
may be mentioned that the device of the present preferred embodiment 
manufactured by the inventor had a PV ratio of more than 30 when operated 
at a room temperature. When the difference in work function between 
electrode materials for the anode 2 and the cathode 4 is increased, 
rectifying characteristics are created. However, when the electrode 
materials for the electrode 2 and the cathode 4 are made to have the same 
level of the work function, no rectifying characteristic could be 
obtained, and peaks/valleys will appear in the voltage-current 
characteristics for both the forward and reverse directions. 
Since the electronic carrier-transporting lower molecular organic compounds 
and the electrically insulating organic polymers have enclosed structures, 
there is almost no surface level. Further, since the molecular-doped 
negative-resistance device of the present invention is totally constructed 
of organic material, individual molecules involve no difference in thermal 
expansion coefficient and the device is therefore thermally stable. In 
addition, because of the fact that the polymer matrix is an organic 
polymer material, the device has a high mechanical strength. 
The molecular-doped negative-resistance device of the present preferred 
embodiment does not require any process of alternately laminating crystals 
of different compositions upon one another in an ultra-high vacuum state, 
and is therefore very simple in construction, well adaptable for finer 
size reduction, and has good workability. Further, the device does not 
require the use of ultra-high vacuum as used in the MBE method, or of a 
vacuum vessel or organic gas as used in the MOCVD method, nor does it 
require the use of a costly film forming apparatus. In addition, since the 
device is a single device, the device requires formation of doped polymer 
films and electrodes only. Thus, the molecular-doped negative-resistance 
device offers an exceptional advantage that it can be manufactured at very 
lower cost. 
EXAMPLES 
First Example 
As shown in FIGS. 1 and 2, an anode 2 made of ITO (indium tin oxide) is 
formed on a glass substrate 1, then a TPD-doped PVCz thin film which 
defines a molecular-doped layer 3 is formed on the anode 2, and then a Mg 
layer for the cathode 4 is vacuum deposited on the molecular-doped layer 
3. The TPD used in the molecular-doped layer 3 is an amorphous, hole 
transporting organic compound, and PVCz is an amorphous, electrically 
insulating organic polymer. FIGS. 3 and 5 respectively show molecular 
structures of TPD and PVCz used in the present example. 
FIGS. 7, 8, 9 and 10, each show the principle of operation of a 
molecular-doped negative-resistance device having a negative-resistance, 
and FIGS. 11 and 12 respectively show the process of tunnel injecting an 
electronic carrier from the anode 2 and that from the cathode 4. In this 
conjunction, reference is made to FIG. 11 which is a diagram showing an 
energy level at the time when positive bias voltage is applied to the 
device, between the ITO electrode as the anode 2 and the Mg electrode as 
the cathode 4. 
As shown in FIG. 11, a hole is tunnel-injected at room temperature from a 
spot adjacent the Fermi level of ITO into a TPD molecule within the 
molecular-doped layer 3 of TPD-doped PVCz. As shown in FIG. 9, the 
electric conductivity of TPD is higher than the electric conductivity of 
PVCz. Therefore, the potential gradient of TPD is lower than that of PVCZ. 
The hole tunnel-injected from the anode 2 of an ITO electrode into TPD 
polarizes the surrounding thereof. As a result, the energy level of an 
occupied HOMO becomes deeper, and the hole tunnels to an empty HOMO which 
comes close thereto by an external electric field. When an applied voltage 
reaches 3.5 V, the Fermi level of the ITO electrode and the level of the 
empty HOMO become even, and also the occupied HOMO and the empty HOMO 
become equal in the level, this leads to a large current peak. 
FIGS. 13 and 14 are energy band diagrams for reading energy level 
differences between constituent materials of various negative-resistance 
devices shown in examples of the present invention. In the present 
example, the height of a barrier against hole injection between PVCz and 
TPD is about 0.5 eV. 
Next, the method for manufacturing the molecular-doped negative-resistance 
device in the present example of the present invention is described 
hereinbelow. On the anode 2 of an ITO electrode having a thickness of 
about 150 nm vapor-deposited by spattering on glass substrate 1 of FIG. 1, 
a TPD molecule-doped thin film of PVCz is formed by means of the dip 
coating technique to the thickness of about 50 nm. Then, the thin film is 
dried with a solvent saturated vapor pressure so that any pin hole 
formation in the thin film can be prevented. Then, the cathode metal 4, 
namely, Mg having a thickness of 50 nm and Ag having a thickness of 200 nm 
are vapor deposited by vacuum spraying in an order of Mg and Ag, and the 
device is completed. The vapor deposition of Ag is intended to prevent 
oxidation of Mg. Where Mg and Ag are vapor co-deposited, the 
anti-deterioration characteristics of the device can be further enhanced. 
The thickness of each layer was measured by means of an ellipsometer. The 
doping concentration of TPD in the present example is about 29 wt % 
relative to the polymer matrix, i.e., PVCz, the average distance between 
molecules is about 0.91 nm, and the molecular length of TPD is 1.8 nm to 
the maximum. The formation of above described thin film for 
molecular-doped layer 3 may be carried out by the spin coating technique. 
The concentration of the dopant is not limited to 29 wt %. 
The DC voltages changing from 0 V to +10 V were applied to the device at a 
room temperature (scan speed: 20 mV/sec), and negative-resistance (or 
negative electric conductance) characteristics were obtained in the 
forward voltage-current characteristics shown in FIG. 15. As the bias 
voltage was increased, the current also increased at a voltage level of 
about 1 V and higher until the maximum value was reached at about 3.5 V. 
This peak current density was about 150 mA/cm.sup.2. Subsequently, it was 
observed that the current decreased due to negative-resistance and then 
began to increase at a voltage level close to 7 V. The difference between 
the peak voltage and the valley voltage was larger than that of an Esaki 
diode by about order of magnitude. The reverse current was comparatively 
small, say, on an order of 1 .mu.A/cm.sup.2. When the voltage level was 
.+-.6 V, good rectification characteristic was showed with a rectification 
ratio of 300. The device exhibited very good reproducibility with respect 
to these voltage-current characteristics. The material of the anode 2 in 
the present instance is not limited to ITO, and any other material is 
acceptable as long as value of its work function is close to that of the 
HOMO of TPD. For example, such other material may be Au, Ag or C. The 
material of the cathode 4 is not limited to Mg, and any other material is 
acceptable if its work function value is substantially different from that 
of LUMO of TPD. For example, such other material may be Al, Li, or a 
Mg--Ag or Al--Li alloy having high chemical stability. 
Next, the switching characteristics of the device when current driven are 
shown in FIG. 16. When the drive current is increased from zero, a voltage 
of about 2 V is generated at 75 mA/cm.sup.2. When the current is further 
increased, a voltage of about 9 V is suddenly generated at a similar 
current density. Conversely, as the drive current is decreased, the 
voltage level goes back to zero volt straight from 6 V or so. As may be 
apparent from the switching characteristics illustrated in FIG. 16, the 
device provides hysteresis characteristics. 
Second Example 
While the description of the first example concerns the case in which the 
electrically insulating organic polymer used is PVCz (poly 
(N-vinylcarbazole)), amorphous PS (polystyrene) may be used instead of 
PVCz to give the same negative-resistance characteristics in a manner 
similar to that in the case where PVCz is used. In the present example, 
the construction of the device is such that in the construction shown in 
FIG. 1, the anode 2 is made of ITO; the molecular-doped layer 3 is made of 
a TPD-doped PS, and the cathode 4 is made of Au. TPD of the 
molecular-doped layer 3 is a hole transporting amorphous material, and it 
is doped in PS (polystyrene) of an electrically insulating material, then 
a multiple barrier type molecular doping structure is formed. FIGS. 3 and 
6 respectively show molecular structures of TPD and PS used in the present 
example. 
Where a hole transporting lower molecular-doped polymer thin film is 
sandwiched between electrode materials each having a large work function, 
such as ITO, Au or the like, peaks/valleys, that is, a negative-resistance 
is observed also in the reverse direction as shown in FIG. 17. The wave 
form of reverse current is smaller because the work function of Au is 
smaller than the work function of ITO, and because the quantity of hole 
injection from the electrode is smaller. 
FIG. 11 is a diagram showing an energy level at the time when a positive 
bias voltage is applied to the device between the anode 2 of an ITO 
electrode, and the cathode 4 of an Au electrode. FIG. 11 illustrates holes 
being tunnel-injected from Fermi level or adjacent level of ITO into TPD 
of the TPD-doped PS. As is apparent from FIGS. 9 and 10, the electric 
conductivity of TPD is higher than that of PS and, therefore, the 
potential gradient of TPD is lower than that of PS. A hole tunnel-injected 
from the anode 2 of the ITO electrode into TPD polarizes its surroundings. 
As a result, the energy level of the occupied HOMO becomes deeper, and the 
hole tunnels into an empty HOMO which has approached under the influence 
of an external electric field. As the applied voltage increases to 3.6 V, 
the Fermi level of ITO and the level of the empty HOMO, as also the level 
of an occupied HOMO and the level of the empty HOMO, become even with each 
other, and thus there occurs a large current peak. According to the energy 
band diagrams for ITO, TPD, PS and Au shown in FIGS. 13 and 14, the 
barrier height between PS and TPD against hole injection is about 1.5 eV, 
and PV ratio is about 30. 
The method for manufacturing the device shown in the present example is as 
follows. A TPD-doped PS thin film is formed to a thickness of about 50 nm 
by the dip coating technique on the anode 2 of the ITO electrode of about 
150 nm in thickness which is vapor deposited by spattering on a glass 
substrate shown in FIG. 1. Then, the thin film is dried under a saturated 
solvent vapor pressure so that pinhole formation in the thin film can be 
prevented. Thereafter, cathode metal 4 or Au (50 nm thick) is vacuum vapor 
deposited on the thin film to complete the manufacturing of the device. In 
the present example, the doping concentration of TPD is about 29 wt % 
relative to the PS, i.e., the binder, average distance between molecules 
is about 0.94 nm, and the molecular length of TDP is 1.8 nm, maximum. 
Manufacturing of the thin film may be carried out by spin coating. It is 
to be noted that the dopant concentration is not limited to 29 wt %. 
The DC voltage charging from 0 V to +10 V was applied to the device (scan 
speed: 20 mV/sec) at room temperature. As a result, negative-resistance 
(or negative electric conductance) characteristics were exhibited in the 
forward voltage-current characteristics shown in FIG. 17. As bias voltage 
increased, electric current began to increase in the vicinity of 0 V and 
reached a maximum value in the vicinity of 3.6 V. The peak current density 
was about 225 mA/cm.sup.2. Subsequently, it was found that the current 
decreased due to the negative-resistance and began to increase in the 
vicinity of 7 V. The difference between the peak voltage and the valley 
voltage was more than 2 V. The reproducibility of the voltage-current 
characteristics was very satisfactory. As may be seen from the present 
example, where the lower molecular organic compound doped in the organic 
polymer is a hole transporting material and where a HOMO of the compound 
is close to the work functions of the anode and cathode, 
negative-resistance will occur in both forward and reverse directions. 
Such negative-resistance in both directions will also occur in the case 
where the lower molecular organic compound doped in the organic polymer is 
an electron transporting material and where a LUMO of the compound is 
close the work functions of the anode and cathode. 
Third Example 
The construction of the device in the present example is such that in FIG. 
1 the anode 2 is made of ITO, the molecular-doped layer 3 is made of 
Alq.sub.3 -doped PVCz, and the cathode 4 is made of Mg/Ag. The Alq.sub.3 
(8-hydroxy-quinoline aluminum) in the molecular-doped layer 3 is an 
electron transporting amorphous material such that a multiple barrier type 
molecular doping structure is formed by doping the material in the PVCz 
(poly (N-vinylcarbazole)), an electrically insulating material. FIG. 4 
shows a molecular structure of Alq.sub.3 used in the present example. 
FIG. 12 is an energy level diagram which shows the energy level at the time 
when negative bias voltage is applied to the device between the cathode 4 
of an Mg electrode, and the anode 2 of an ITO electrode, electrons being 
tunnel-injected into the Alq.sub.3 of the Alq.sub.3 -doped PVCz from the 
Fermi level or an adjacent level of the Mg electrode. As shown in FIGS. 7 
and 8, the electric conductivity of Alq.sub.3 is higher than the electric 
conductivity of PVCz and, therefore, the potential gradient of Alq.sub.3 
is lower than that of PVCz. Each electron which is tunnel-injected from 
the Mg electrode of the cathode 4 into Alq.sub.3 polarizes the 
surroundings of the Alq.sub.3. As a result, the level of the occupied LUMO 
which has trapped an electron becomes deeper, and the electron tunnels 
into an empty LUMO which has approached under the influence of an external 
electric field. As the applied voltage increases to 4 V, the Fermi level 
of Mg and the level of the empty LUMO, as also the level of an occupied 
LUMO and the level of the empty LUMO, become even with each other, and 
thus there occurs a large current peak. FIGS. 13 and 14 are energy band 
diagrams for ITO, Alq.sub.3, PVCz, and Mg. The barrier height between PVCz 
and Alq.sub.3 against electron injection is about 1.6 eV, and PV ratio is 
about 11. 
The method for manufacturing the device shown in the present example is as 
follows. An Alq.sub.3 molecule-doped PVCz thin film is formed to a 
thickness of about 50 nm by the dip coating technique on an ITO electrode 
of anode 2 of about 150 nm in thickness which is vapor deposited by 
spattering on a glass substrate shown in FIG. 1. Then, the thin film is 
dried under a saturated solvent vapor pressure so that pinhole formation 
in the thin film can be prevented. Thereafter, cathode metals 4, that is, 
Mg (50 nm thick) and Ag (200 nm thick), are vacuum vapor deposited on the 
thin film to complete the device as such. In case that Mg and Ag are 
co-deposited, the device can have improved resistance to deterioration. In 
the present example, the doping concentration of Alq.sub.3 is about 29 wt 
% relative to the Alq.sub.3 content of the polymer matrix, average 
distance between molecules is about 1.01 nm, and the molecular length of 
Alq.sub.3 is 0.75 nm, maximum. Manufacturing of the thin film may be 
carried out by spin coating. 
The DC voltage charging from 0 V to +12 V was applied to the device (scan 
speed: 20 mV/sec) at room temperature. As a result, negative-resistance 
(or negative electric conductance) characteristics were exhibited in the 
forward voltage-current characteristics shown in FIG. 18. As bias voltage 
increased, electric current began to increase in the vicinity of 0 V and 
reached a maximum value in the vicinity of 4 V. The peak current density 
was about 50 mA/cm.sup.2. Subsequently, it was found that the current 
decreased due to the negative-resistance and began to increase in the 
vicinity of 7 V. The difference between the peak voltage and the valley 
voltage was more than 2 V. The reproducibility of the voltage-current 
characteristics was very satisfactory. Where the material of the anode 2 
in this example is smaller in work function than HOMO of Alq.sub.3 and 
where the difference is substantial, the anode material is not limited to 
ITO and may be Al or Cu, for example. Where the material of the cathode 4 
is close to LUMO of Alq.sub.3 in work function, the material is not 
limited to Mg, and may be, for example, Al, Li, or chemically highly 
stable Mg--Ag alloy or Li--Al alloy. 
Although poly (N-vinylcarbazole) and polystyrene were used as polymer 
matrix in the foregoing examples, other materials may be used as such 
without limitation if the material is an organic polymer material which is 
soluble in organic solvents, well compatible with lower molecular organic 
compounds, and does not adversely affect the mobility of electronic 
carriers. For example, preferred polymer materials include polycarbonate 
(PC), polyvinyl chloride (PVC), polyether sulfone (PES), and polymethyl 
methacrylate (PMMA). The lower molecular organic compounds are not limited 
to TPD and Alq.sub.3 as long as the compound has a molecular length of nm 
order and carrier transporting capability. As examples of hole 
transporting materials may be mentioned organic dye molecule, such as 
triphenylamine derivative (TPA), quinacridone (QA), diamine derivative 
(NSD), bis-triphenylaminestil derivative (BTAS), butadiene derivative 
(DEAB), pentaphenyl cyclopen (PPCP), and distyryl biphenyl derivative 
(DPVBi). Examples of electron transporting materials include organic dye 
molecule, such as styryl derivative (ST-1), 9, 10-bis-styryl anthracene 
derivative (BSA), oxadiazole derivative (OXD), distyryl benzene derivative 
(DSB), perylene derivative (PV), and 1, 2, 4-triazole derivative (TAZ); 
and quinolinol-based metal complexes, such as Be-benzoquinolinol complex 
(Beq.sub.2), and gallium 8-quinolate (GaQ). 
Doping of lower molecules into the polymer may be carried out without using 
a solvent, say, by employing a dry method, such as a vacuum vapor 
deposition method or an ionized vapor deposition method of, for example, 
poly (N-vinylcarbazole). 
First Application Example 
FIG. 19 is a circuit diagram showing a circuit configuration of a tuning 
oscillation circuit as a first application example of the molecular-doped 
resistance device shown in FIG. 1, and FIG. 20 is a circuit diagram 
showing an equivalent circuit. FIG. 21 is a graph showing an operating 
point and oscillatory growth in the tuning oscillation circuit. 
In FIG. 19, a capacitor C is connected in parallel with the molecular-doped 
resistance device TD, and further, the capacitor, an inductor L, a load 
resistance R.sub.L, and a DC bias supply 20 are connected in series, then 
the tuning oscillation circuit is formed. In the equivalent circuit shown 
in FIG. 20, the molecular-doped negative-resistance device TD may be 
depicted as a parallel circuit of a negative electric conductance -Gd and 
a capacitor Cd. 
In the first application example, in order to make an oscillation, it is 
necessary that the circuit must have an operating point at P.sub.0. in the 
negative-resistance (or negative electric conductance) region, and that 
the load resistance R.sub.L be 1/R.sub.L &gt;.vertline.Gd.vertline., that is, 
R.sub.L &lt;1/.vertline.Gd.vertline. as shown in FIG. 21. The reason for this 
is that if 1/R.sub.L &lt;.vertline.Gd.vertline., three operating points exist 
so that the oscillated signal is clamped so as to prevent any oscillation 
operation. Therefore, as illustrated in FIG. 19, a parallel resonant 
circuit configuration is employed such that the load resistance R.sub.L is 
connected in series to the inductor L, with the molecular-doped resistance 
device TD connected in series to the capacitor C connected as above said. 
In FIG. 20, the equivalent circuit is illustrated in such a way that the 
series resistance of the molecular-doped negative-resistance device TD is 
disregarded. The equivalent circuit for the molecular-doped 
negative-resistance device TD is shown as a parallel circuit of Cd 
(barrier capacitance) and -Gd (gradient of straight line AB). When the 
supply voltage E is applied to the parallel resonance circuit so that the 
LC oscillator using the molecular-doped negative-resistance device TD can 
operate in the negative-resistance region, oscillation conditions are as 
follows: 
EQU -Gd+j.omega.(C+Cd)+1/(R.sub.L +j.omega.L)=0 (1) 
In the above equation (1), the following equation (2) is used. 
EQU Q=(.omega.L)/R.sub.L (2) 
EQU 1/(R.sub.L +j.omega.L)=1/R+1/j.omega.L' (3) 
Where Q&gt;1, the following equation is obtained. 
EQU R=R.sub.L (1+Q.sup.2).apprxeq.R.sub.L Q.sup.2 (4) 
EQU L'=L(1+1/Q.sup.2).apprxeq.L (5) 
For oscillation conditions, the following equation is obtained from above 
equations (1) through (5). 
EQU .omega.=1/(L'(C+Cd)).sup.1/2 (6) 
EQU R&gt;1/.vertline.Gd.vertline. (7) 
Therefore, oscillating frequency f and power conditions are respectively 
expressed by the following equations. 
EQU f=(1/2).pi.(L(C+Cd)).sup.1/2 (8) 
EQU R.sub.L .ltoreq..vertline.Gd.vertline.L/(C+Cd) (9) 
In the above equation (9), the condition "R.sub.L 
=L.vertline.Gd.vertline./(C+Cd)" is ideal for use as a power condition. In 
practice, however, the condition is set to "R.sub.L 
&lt;.vertline.Gd.vertline.L/ (C+Cd)". 
Next, an oscillating operation will be explained with reference to FIG. 21. 
At the initial stage of oscillation, the absolute value of gradient Gd' 
(gradient of straight line QQ') in the characteristic curve is larger than 
the conductance 1/R.sub.L of the resonance circuit, and the quantity of 
supply energy is larger than the quantity of lost energy. Therefore, the 
oscillation tends to grow. Thereafter, as the swing ranges of voltage and 
current become larger, the value of Gd' gradually tends to become smaller. 
When the swing on the characteristic curve tends to occur in the range of 
A to B, the gradient of the characteristic curve is Gd (gradient of 
straight line AB). 
When the absolute value of the gradient Gd becomes just equal to 1/R.sub.L, 
the lost energy and the supplied energy are balanced so that the amplitude 
of the swing becomes constant, resulting in a stationary state. The 
amplitude of the oscillation amplitude is determined by the voltage range 
between the peak voltage and the valley voltage in the negative-resistance 
region shown in FIG. 21. The oscillation amplitude of the device is about 
2 V, which is one digit larger as compared with Esaki diode. For the 
oscillation circuit, a circuit arrangement in which the inductance L and 
the load resistance RL are connected in parallel is also conceivable. 
Second Applicable Example 
FIG. 22 is a circuit diagram showing a circuit configuration of a pulse 
generating circuit as a second application example of the molecular-doped 
negative-resistance device shown in FIG. 1, and FIG. 23 is a graph showing 
operating points and a DC load line in the pulse generating circuit. FIG. 
24 is a signal waveform diagram showing a trigger pulse current and a 
generated pulse voltage which appear in the pulse generating circuit when 
a positive trigger pulse current is flowed into the circuit. FIG. 25 is a 
signal waveform diagram showing a trigger pulse current and a generated 
pulse voltage which appear in the pulse generating circuit when a negative 
trigger pulse current is flowed into the circuit. 
In the circuit shown in FIG. 22, a series circuit of a switch SW and a load 
resistance R.sub.L is connected in parallel to the molecular-doped 
negative-resistance device TD, and a junction between the switch SW and 
the anode of the molecular-doped negative-resistance device TD is made to 
serve as an input point for trigger pulse current. A series circuit of an 
inductor L, a series resistance Rb and a DC bias power supply 30 is 
connected in parallel to the series circuit of switch SW and load 
resistance R.sub.L. 
This pulse generating circuit has a circuit configuration such that the 
inductor L and the series resistance Rb with a resistance value smaller 
than the negative-resistance value (1/.vertline.Gd.vertline.) are 
connected in series to the molecular-doped negative-resistance device TD. 
As shown in FIG. 23, if the bias voltage E applied is lower than voltage 
E.sub.1, the intersection point P.sub.1 becomes a stable operating point. 
If the bias voltage E is higher than voltage E.sub.2, the point P.sub.2 
becomes a stable operating point. If an input pulse current with an 
amplitude of dI.sub.1 or more is applied to the molecular-doped 
negative-resistance device TD in the state of the operating point P.sub.1, 
the molecular-doped negative-resistance device TD enters a 
negative-resistance (conductance) region and becomes unsteady. However, 
because of the inductance of the series inductor L, the current could not 
rapidly be decreased, and the operating point moves from P.sub.1 to 
P.sub.2 as shown by a broken line shown in FIG. 23. Along with this 
movement, there occurs a rapid increase in voltage V at the 
molecular-doped negative-resistance device TD. However, bias voltage E is 
not so high as to permit the operating point to stay at that point. 
Therefore, the current I flowing in the molecular-doped 
negative-resistance device TD is gradually reduced. Thus, the operating 
point moves from P.sub.2 to P.sub.3 and then again passes through the 
negative-resistance region to switch to the operating point P.sub.4. 
Accompanying with this, the output voltage is reduced and then the device 
returns to the initial state of the operating point P.sub.1, becoming thus 
stabilized. In this way, each time trigger pulse is applied, a positive 
output pulse can be obtained as shown in FIG. 24. 
In a manner similar to that of above, in the case where the stabilization 
point is positioned at the point P.sub.3, upon application of a negative 
trigger pulse having an amplitude of dI.sub.2 or more, the operating point 
moves in the sequence of P.sub.3 .fwdarw.P.sub.4 .fwdarw.P.sub.1 
.fwdarw.P.sub.2, becoming stabilized at the point P.sub.3. In this case, 
as shown in FIG. 25, a negative pulse voltage can be generated. 
The range of output pulses is mainly determined by the inductance value of 
the series inductor L. If the inductance value is increased, the pulse 
range becomes wider. The leading time of the pulse voltage changes in 
correspondence with the switching time from P.sub.1 to P.sub.2 so that the 
greater the difference between the peak current and the valley current, or 
the PV ratio is, and the smaller the barrier capacitance is, the shorter 
the leading time is. The trailing time thereof changes in correspondence 
with the switching time from P.sub.3 to P.sub.4 so that the smaller the 
valley resistance defined by the valley voltage to valley current ratio 
is, and the smaller the barrier capacitance is, the shorter the trailing 
time is. When the load resistance R.sub.L is connected in parallel to the 
molecular-doped negative-resistance device TD, the output pulse voltage 
will decrease with the decrease in the resistance R.sub.L. 
Besides the above described application for pulse generating circuits, a 
flip-flop circuit having a load resistance R.sub.L connected in parallel 
to the molecular-doped negative-resistance device TD may be considered 
such that a trigger pulse current is caused to operate in conjunction with 
a constant current that is comparatively lower than peak current while the 
constant current is flowed into the circuit. 
In the above-mentioned preferred embodiments and examples, the anode 2 and 
the cathode 4 are configured to have a strip-like shape in such a way that 
they intersect with each other at right angles as shown in FIG. 1. 
However, the present invention is not limited to this. The anode 2 and the 
cathode 4 may be formed on the entire surface thereof, or may be formed in 
a lattice-like pattern. 
INDUSTRIAL APPLICABILITY 
As described above, the molecular-doped negative-resistance device 
according to the present invention comprises a molecular-doped layer made 
of an electron transporting lower molecular organic compound, said 
molecular-doped layer being formed to be sandwiched between a pair of 
electrodes, 
wherein respective molecules of said electron transporting lower molecular 
organic compound are isolated from one another by an electrically 
insulating organic polymer, 
wherein said molecular-doped negative-resistance device has a 
negative-resistance. 
Accordingly, the device includes an electrically insulating organic polymer 
in which electronic carrier transporting lower molecular organic compound 
is doped, and then the electrodes sandwiches the same, namely, the 
electrodes includes the anode metal having a larger work function, and the 
cathode metal having a smaller work function or a cathode metal having a 
larger work function. The electrically insulating organic polymer and the 
lower molecular organic compound serve as a potential barrier and as a 
carrier transporting molecule, respectively. The rectifying 
characteristics can be obtained by controlling the barrier against tunnel 
injection at the interface between the electrode and the lower molecular 
organic compound to thereby inject only one of hole and electron carriers. 
The negative-resistance can be obtained through polarization due to 
carrier trap of the lower molecular organic compound in the process of the 
tunnel injection at the electrode interface and in the process of the 
tunnel electric conduction of tunnel-injected hole or electron through the 
bulk, and also by relative positions of the LUMO level, the HOMO level, 
and the Fermi level of the electrode metals which vary due to external 
electric field. The molecular-doped negative-resistance device exhibits 
good negative-resistance characteristic, good switching characteristic, 
and good rectification characteristic at a room temperature, and can 
therefore be used in constructing switching devices and logical devices. 
In the molecular-doped negative-resistance device according to the present 
invention, little or no surface level is formed at the interface between 
the electrically insulating organic polymer and the lower molecular 
organic compound. Therefore, the device involves little or no 
deterioration due to such surface level. The device affords a substantial 
freedom of material selection because many kinds of organic materials can 
be used. The molecular device of the present invention has high mechanical 
strength and thermal stability because an organic polymer material is used 
therein. Further, because of the fact that molecules of a lower molecular 
organic compound such as TPD are doped in the electrically insulating 
organic polymer, agglomeration of such lower molecules is inhibited. 
Therefore, the interaction of carrier transporting molecules can be 
minimized, the device being thus prevented from deterioration. 
The interface between the electrically insulating organic polymer and the 
lower molecular organic compound is subject to the influence of moisture, 
but by coating the entire device with resin or the like for protection it 
is possible to prevent deterioration due to the moisture. The 
molecular-doped negative-resistance device according to the present 
invention can be widely used in applications such as oscillator, switching 
device, and logical element. Further, the device is very simple in 
construction and can be formed in a thin film configuration in the 
atmosphere. Therefore, the device has a good processability. It is 
necessary, however, to use good care for moisture and dust control in the 
process of film forming. Moreover, the present invention does not require 
the use of any costly ultra-high vacuum apparatus and this enables 
industrial mass production of the device at lower manufacturing cost.