JPS59198766A - Ferrodielectric semiconductor device - Google Patents

Abstract

PURPOSE:To obtain the titled device of a wide range of application as various kind of sensors, etc. by enabling to vary the characteristic of signal conversion and the performance such as sensitivity by utilizing the variation of electric properties accompanying the phonon softening phenomenon of the ferrodielectric. CONSTITUTION:An Fe ion implanted doped region 2 is manufactured in the surface of an SrTiO2 substrate 1 that is ferrodielectric substance, electrodes 3 and 4 to input and output an electric signal are formed at both ends thereof, and lead wires 5 and 6 are connected. in this substrate structure, the ion implanted doped region 2 has the electric resistance reduced down to a value of the degree that a semiconductor substance has, thus facilitating the measurement and detection of the electric resistance. Both of the substrate 1 and the doped region 2 have each critical temperature at which abnormality is observed in the electric resistance. However, those values becomes different by the introduction of the impurity to the doped region 2. In other words, the electric resistance shown by the doped region 2 can be adjusted by controlling the kind of the impurity and its amount.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to a device that utilizes the electrical properties of a ferroelectric material to detect physical changes occurring in a new body using electrical signals.

<Background of the Invention> Examples of ferroelectric materials include ferroelectric substances, antiferroelectric substances, paraelectric substances, and ferrielectric substances. Such a ferroelectric material undergoes a phase transition accompanied by a change in crystal structure at a certain temperature Tc (critical substance). The critical phenomenon accompanied by such a phase dislocation is thought to be due to the following cause resulting from the instability of lattice vibration.

Generally, there are acoustic phonons and optical phonons in the lattice vibration of materials, and the energy of each phonon depends on the wave vector IK. The critical phenomenon observed in the above-mentioned materials mainly originates from the instability of optical phonons among the above-mentioned lattice vibrations. That is, the critical phenomenon occurs when the energy (or frequency) of a specific optical phonon suddenly decreases near a specific temperature.

As mentioned above, the phenomenon in which the energy of phonons decreases is generally called 1' phonon softening.In the above ferroelectric materials, the wave vector 1 has the following effect in space: 1f12=
The optical phonon specified by (ooo) is a substance that causes softening or a ferroelectric substance, and the optical phonon specified by the positive value of the wave vector at the boundary of the first Brillouin zone is a substance that causes softening. It is a ferroelectric substance. In addition to ferroelectric materials and antiferroelectric materials whose wave vector 1k is expressed by the above values, there are also materials that cause optical phonon softening when the wave vector is old or has a value other than the above values. An example of this is 5rTi03 with a critical temperature near 110°.
Figure 1 shows the temperature dependence of the phonon energy of IP, = (7,7,7)F25.

When phonons soften, the physical properties of matter change accordingly. For example, FIG. 2 shows the temperature dependence of the linewidth of spin resonance absorption of Fe3+ ions for a sample in which Fe3+ is added as an impurity to 5rTi03.

As is clear from the figure, when the phonon softens, a change appears in the spin resonance absorption, and the absorption linewidth abnormally increases near 115°. This abnormal phenomenon accompanying phonon softening also appears in electrical resistance, and the increase in electrical resistance is △
At a temperature T near the critical temperature Tc, R can be qualitatively expressed as follows.

The above increase in electrical resistance △R varies depending on each substance, but
If △R is plotted against temperature T, it will look like the curve shown in Figure 3, where the electrical resistance increases significantly near the critical temperature Tc, and the softening of phonons can be confirmed as a change in electrical resistance. .

However, when an electric field is applied externally to a substance that causes phonon softening as described above, the energy of phonon softening changes, qualitatively changing the degree of the solid line in Figure 4, and increasing the critical temperature. The change also results in a change in electrical resistance in the ferroelectric.

The change in electrical properties associated with the phonon softening phenomenon of a ferroelectric as described above can be used as a means for converting a physical quantity into an electrical signal by relating it to a physical quantity that can cause a change in phonon energy.

<Objective of the Invention> The present invention provides a new and useful ferroelectric semiconductor device by utilizing changes in electrical properties accompanying the phonon softening phenomenon of ferroelectrics.

<Example 1> Ferroelectric substance 1 As a ferroelectric substance that can be classified into antiferroelectric substances, paraelectric substances, and ferrielectric substances, for example, S
rT i03 , L 1Nb03 , BaT i0
3.

)■ There are insulators such as 03 and semiconductors with a narrow energy forbidden band such as 5nTe, but among these materials, Sr'
A case will be described using Fi03.

First, we will explain the structure of a ferroelectric semiconductor device to confirm the abnormal phenomenon of electrical resistance caused by phonon softening that occurs at a certain temperature. In FIG. 5, 5rTi, which is a ferroelectric material,
A doped region 2 having a thickness of about 3 μm to 5 μm is created by implanting Fe ions at a concentration of about 10/min on the surface of the substrate 1 of 03, and an electrical signal is placed at one end and the other end of the doped region 2. An electrode 3.4 for this purpose is formed and a lead wire 5.6 is connected thereto.

In the above ferroelectric substrate structure, 5iTi03 of the substrate 1
Although by itself it is an insulator with a band width of about 3 eV, it was ion-implanted by implanting Fe ions.

The doped region 2 has a reduced electrical resistance to a value similar to that of a semiconductor material 9, making it easier to measure and detect the electrical resistance.

Both the substrate 1 and the doped region 2 have critical temperatures T el and T c2 at which an abnormality is observed in electrical resistance, but these values become different depending on whether impurities are introduced into the doped region 2 or the like. That is, by controlling the type and amount of impurities, the electrical resistance exhibited by the doped region 2 can be adjusted.

FIG. 6 measures the warm dependence of the electrical resistance in the ion-implanted region and shows the abnormal change in resistance due to phonon lift. As is clear from the figure, the electrical resistance increases abnormally near 103°. A similar phenomenon occurs when boron other than iron ions is implanted. The reason why the critical temperature is shown as 103°K, which is slightly closer to the lower temperature side than 110° in FIG. 6, is considered to be due to the dependence of the critical temperature Tc on the carrier concentration.

The critical temperature Tc of a ferroelectric material at which phonon softening occurs has a dependence on carrier concentration; for example, concentration dependence occurs in other ferroelectric materials. For example, by adding impurities to a certain ferroelectric material and controlling its carrier concentration, it is possible to make Tc close to room temperature, or even to a temperature other than room temperature. The electrical properties of ferroelectric materials doped with impurities as described above can be used to construct new electrical signal output elements, sensors, etc.

More specific examples will be described below.

<Example 2> This example is configured as an electrical signal conversion device, and in FIG. 7, a substrate 1 made of the above-mentioned ferroelectric material
1 is an insulator that softens at temperature Tc1. A thin semiconductor layer 12 having the same crystal structure as the substrate 11 and high electrical conductivity is formed on the surface of the substrate 11. The semiconductor layer 12 is formed using ion implantation, molecular beam epitaxial method, etc., and can be either n-type or p-type depending on the type of impurity introduced, and may be of either conductivity type.

The semiconductor layer 12 also causes phonon softening, but the substrate 1
Since the carrier concentration is different from Tel1, the critical temperature Tc2 of the semiconductor layer 12 usually appears different from the above Tel. The carrier concentration of the semiconductor layer 12 is determined in consideration of the performance of the electrical signal conversion device, and the type and type of carriers are determined so that the outside temperature and the critical temperature Tc2 in the environment in which the electrical signal conversion device is operated are close to each other. It is desirable to select the appropriate concentration from the viewpoint of device sensitivity. In the substrate 11, an input region 13 and an output region 14, which serve as input/output portions for electrical signals, are formed in succession to the doped region which becomes the semiconductor layer 12, and impurities are introduced at the same time as the formation of the semiconductor layer 12 or in a separate process. It is formed by - Metal electrodes 15 and 16 are formed in ohmic contact with the input region 13 and the output region 14, respectively, and lead wires 1, 7, and 18 are led out. In order to apply an electric field to the semiconductor layer 12, a thin insulating film 19 is deposited on the surface of the semiconductor layer 12, and an electrode 20 is formed on the insulating film 19 to form a field effect transistor structure.

In a device having the above structure, a voltage E is applied to the electrode 20.
When applied, an electric field is generated in the semiconductor layer 12, and the electrical resistance of the semiconductor layer 12 changes. The sensitivity of this electrical resistance to the electric field increases as the value of the critical temperature T c 1 of the semiconductor layer 12 approaches the outside temperature, and a slight fluctuation in the electric field can be extracted as a relatively large change in the resistance value. The current between lines 17 and 18 is output as a value controlled by the voltage applied to electrode 8.

Embodiment 3 FIG. 8 is a cross-sectional view showing another embodiment of the present invention, in which a pressure is applied 1η as a means of controlling the electrical resistance of a semiconductor layer formed by doping a ferroelectric material with impurities. It is an electrical signal conversion device.

In Example 2, an electric field is applied to a ferroelectric material that exhibits the phonon softening phenomenon, and the change in electrical resistance is extracted as an output. It can also be obtained by applying a pressure that exerts substantially the same effect as an electric field on the ferroelectric layer 21.
1'r from Hiroshi 1. Finally, 11 impurities or doped ferroelectric layers 1 and 2 layers are formed, and the semiconductor layer 2
The insulation layer 22 is covered with an insulating layer 223 covering the surface of the semiconductor layer 22. An electric current is provided at both ends of the semiconductor layer 22 by sandwiching the covered area. The input/output electrodes 24.25 are formed by 3, L, , +J1'11J5'i; and when the El-force F is applied to the insulation 11 and 23, , In response to a monthly force of 1'', the phonon softening energy key of the semiconductor layer 22 changes, resulting in a change in electrical resistance and/or a change in the input/output electrode 24.2.
The current drawn between 5 and 1I-) corresponds to the 11 power IS 1]! Li 11゛1 is detected 13 Therefore, pressure 1 is converted into electric current 1 □ and 7By is set as sensor 9-, ril-J- is 5゜, effect, etc. According to the present invention Second, to construct a new electrical signal conversion device using a ferroelectric material, select an impurity to be doped into the ferroelectric material for q and 1 (1N-1f-).
Sorry, I1. -'4.5 Characteristics and Sensitivity of Conversion', U'
By reading the 'Ml: ii:;, it is possible to obtain devices with a wide range of c4.1lllLl by using various sensors.9-';9.

[Brief explanation of drawings]

Figure 1 shows ':17/ in S r 'I' i 03.
'y Tech; (, /l/, '- jA+'+ degree change unchanged, Fig. 2 Ii S r 'I' i 03) Spin co-11i due to A non-softening: M absorption linewidth Figure 3 is a diagram showing the increase in 71J and air resistance due to tumenon softening. Figure 4 is a diagram showing the electric field effect of electrical resistance due to phonon softening. Figure 5 is G. , is a cross-sectional view for explaining one embodiment according to the present invention, FIG. 6 is a diagram showing the 1llllL degree dependence of electrical resistance according to the same embodiment, and FIGS. 1.11.21: Substrate, 2.12.22 Ni-doped ゝV conductor layer, 3.4.15.] (3,2'1.2
5 two electrodes, 19.23: insulation 1 model, l (, electric field, F: output. Temperature T- 1 degree - Temperature r (K) Fig. 6

Claims (1)

[Claims] 1) A ferroelectric layer exhibiting a softening phenomenon in which a specific lattice vibration energy decreases near a critical temperature Tc, and an electric field or mechanical pressure is applied to the ferroelectric layer. A means for controlling electrical resistance is provided, and an electrical signal deriving terminal is provided in the ferroelectric layer, and an electrical signal based on a change in electrical resistance due to a softening phenomenon is extracted from the ferroelectric layer. ferroelectric semiconductor device. 2) The ferroelectric layer has a first critical temperature T on a substrate surface having a first critical temperature Tc1. It has a two-layer structure with a second layer having a second critical temperature TC2 different from I, and has a second critical temperature T. 2. The electric signal is extracted from the second ferroelectric layer having 2.3°. ferroelectric semiconductor device. 3. The ferroelectric semiconductor device according to claim 2, wherein the ferroelectric semiconductor device is an oxide and has the same crystal structure as the substrate. 4) The ferroelectric semiconductor according to claim 2 or 3, wherein the second ferroelectric layer is formed by ion implantation with a single molecular beam or by vapor phase growth. Device. 5) The ferroelectric material according to claim 4, wherein the second ferroelectric layer is formed by implanting boron ions into the surface of the first ferroelectric layer serving as a substrate. Semiconductor equipment. 6) Claims 1, 2, 3, 4 or 6, wherein the critical temperature Tc, Tcl or Tc2 has a temperature difference within 100° with respect to room temperature. The ferroelectric semiconductor device according to item 5.