JPH0342707B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a magnetic sensor used for various measurements and controls in the electronic and mechanical industry fields.

[Conventional technology]

Traditionally, semiconductor materials for magnetic sensors include Si,
Ge or compound semiconductors InSb, InAs, GaAs
Single crystal thin plates, vapor deposited films, epitaxial films, etc.
Ion implanted layers are commonly used.

However, each of the above semiconductor materials had drawbacks. In other words, in order to improve the performance of magnetic sensors, ultrathin film materials with high mobility are required, and indium antimony (InSb), which provides high mobility,
It is difficult to make ultra-thin films with gallium arsenide (GaAs).
Because it is difficult to increase the mobility of ultrathin films using silicon or silicon (Si), there has been a technological limit to improving performance.

[Problem that the invention seeks to solve]

In view of the above points, the present invention has been made with the object of providing a magnetic sensor that has high mobility and can be made into an extremely thin film.

[Means for solving problems]

In general, to improve the performance of semiconductor magnetic sensors, materials and device structures with a large Hall effect are essential, so we will consider the design principle of the Hall element, which is a basic magnetic sensor. In a rectangular Hall element, the Hall output voltage for each of current drive, voltage drive, and power drive is expressed by the following formula.

V _H ＝K _M BI ∝K _H ……(1) = (w/l) μ _H BV ∝μ _H ……(2) = (wK _H μ _H /l) ^1/2 BP ^1/2 ∝(K _H μ _H ) ^1/2 ...(3) Here, l, w, and t are the length, width, and thickness of the element.

I, V, and P are input current, input voltage, and input power.

B is magnetic flux density. K _H is product sensitivity=(=R _H /t=
1/n _s e; P _H is the Hall number. n _s is the carrier surface density. e is the electronic charge). _μH is Hall mobility.

The maximum output is obtained for the maximum input, so
From equation (3), the sensitivity figure of merit MSF (Magnetic−field
MSF=(K _H μ _H ) ^1/2 = μ _H (ρ/e) ^1/2 ∝μ _H ...(4) Here, ρ=1/neμ. Considering the compatibility between the element and the external circuit, it is usually desirable that the characteristic impedance ρ/t be in the range of 10Ω to 10KΩ. In order to increase the sensitivity of the Hall element, it is better to have higher mobility and product sensitivity under these conditions. The product sensitivity is the carrier surface density (product of carrier density and thickness)
Since it is proportional to the reciprocal of , a thin active layer is required for high sensitivity.

On the other hand, when a magnetic sensor is used to detect a minute magnetic field, it is essential that the signal-to-noise ratio (S/N) is high. Hall output and thermal noise V _N
Taking this and defining the S/N ratio, S/N=V _H /V _N =(w/l)μ _H B(P/4kT) ^1/2 ∝μ _H ...(5). Here, k is Boltzmann's constant. T is
element temperature. The first condition for increasing the S/N is that μ _H be large.

To summarize the above, in order to improve the performance of a magnetic sensor under the condition that the internal resistance is within a certain range (for example, considering the compatibility with the external circuit, the desirable internal resistance of the element is 10Ω to 10KΩ), It has been found that a structure in which a high-mobility carrier is confined in an extremely thin active layer is necessary.

Therefore, in the present invention, by providing a heterojunction structure of two types of semiconductors with different band caps, for example, AlGaAs and GaAs, a two-dimensional electron gas layer is formed that confines electrons in a narrow region at the boundary. In addition to using it as a magnetic sensor active layer, a technical means is adopted in which the input and output electrodes of this sensor are formed to have ohmic contact with the two-dimensional electron gas layer at multiple locations.

〔Example〕

Hereinafter, the present invention will be explained in detail based on embodiments shown in the drawings.

FIG. 1 shows a schematic configuration diagram when the present invention is applied particularly to a Hall element. in this case,
Two types of semiconductor layers 4 and 5 with different band gaps
A two-dimensional electron gas layer 6 with high mobility is formed at the heterojunction. In addition, in Figure 1, 2
a, 2b are current terminals for passing current through the Hall element H; 3a, 3b are terminals for supplying magnetic flux density B to the Hall element H;
This is a Hall terminal for taking out the Hall electromotive force _VH generated when a magnetic field of .

Next, the specific structure of the Hall element H and its manufacturing method will be explained.

Figure 2 shows the structure of an AlGaAs layer/GaAs heterojunction semiconductor, in which non-doped GaAs 4, non-doped GaAs 4 and non-doped
Sequential molecular beam crystal growth (MBE) of AlGaAs5a, Si-doped, AlGaAs5b, and Si-doped GaAs5c
It was formed using Note that other methods such as organometallic vapor phase epitaxy, liquid phase epitaxy, etc. may also be used.

As can be seen from FIG. 2, the two-dimensional electron gas layer 2DEG6 is formed on the boundary surface of the non-doped GaAs layer 4 on the non-doped AlGaAs layer 5 side. The reason for providing the non-doped AlGaAs layer 5 is that n
This is to prevent Si in the Si-doped AlGaAs layer 5b from penetrating into the non-doped GaAs 4.

In addition, the Au-
The Ge ohmic electrode 200 is connected to each of the layers 4, 5a, 5.
It is formed to have ohmic contact with b and 5c.

The semi-insulating GaAs substrate for crystal growth can be cleaned using a mixture of concentrated sulfuric acid, hydrogen peroxide, and pure water (volume ratio 4:1:1, liquid temperature 60 degrees Celsius).
The film was etched for a minute, and then thermally etched while being exposed to arsenic vapor in a vacuum chamber for crystal growth. Representative examples of crystal growth conditions are as follows.

1 Ga flux: 6×10 ^-7 Torr 2 As flux: 1.2×10 ^-5 Torr 3 Al flux: 1.4×10 ^-7 Torr 4 Crystal growth temperature: 630 degrees Celsius 5 Crystal growth rate: 1.2 μm/hr (CaAs ) 1.65μm/hr (AlGaAs) 6 1st layer: Non-doped GaAs (500nm) 2nd layer: Non-doped AlGaAs (15nm) 3rd layer: Si-doped AlGaAs (100nm) 4th layer: Si-doped GaAs (10nm) The Si doping concentration is 1×10 ¹⁸ cm ^-3 .

7 Ohmic electrode is AuGe (7% to 12%)/
By alloying the Ni/Au deposited film.

Figure 3 shows the energy band of the prototype heterojunction Hall element. The two-dimensional electron gas layer is filled with electrons supplied from Si-doped AlGaAs, but if there are too many carriers in the AlGaAs layer, i.e. the amount of impurities is too high or the AlGaAs
If the layer is too thick, current will also flow through the AlGaAs layer, which has excess carriers with low electron mobility. This reduces the Hall output. Therefore, AlGaAs
It is important to fabricate heterojunction semiconductors to eliminate excess carriers in the layers.

7 and 8 show a specific example of applying the Hall element with the above configuration to a specific magnetic sensor,
In this example, current terminals 2a, 2b and Hall terminal 3
Au-Ge ohmic electrodes 200 formed on a and 3b
A large number of mesa-shaped holes 201 are provided in the metal thin film 2.
00 is directly brought into contact with the two-dimensional electron gas layer 6 to ensure high mobility, it is possible to improve the linearity of the current-voltage characteristics. Furthermore, by adopting the above structure, many irregularities are created at the boundaries between the ohmic electrode 200 and the semiconductor layers 4 and 5, so the effect of the shape of the Hall element is small compared to the conventional uniform electrode structure. This results in a large Hall output.

Therefore, according to this embodiment, a value equivalent to the maximum figure of merit achievable in single-crystal bulk InSb can be easily obtained in the heterojunction semiconductor magnetic sensor. This is a GaAs epitaxial single crystal.
The performance is more than three times that of the same ion-implanted film, and more than ten times that of Si. Furthermore, one of the features of the present invention is that the heterojunction semiconductor for magnetic sensors is similar to the material for high-speed transistors (e.g., HEMT), making it possible to integrate the sensor and signal processing transistor on one substrate. It is a certain thing. Due to its low noise level and good temperature characteristics, it is expected to lead to the development of high-performance magnetic sensor ICs that cannot be obtained with conventional semiconductor materials, and its use is expected to expand.

Here, the characteristics of the magnetic sensor of this example will be explained based on measured values measured by the inventors.

Figures 4 and 5 show a length of 346μm and a width of 346μm.
The electrical characteristics of a 200μm cruciform heterojunction Hall element are shown. Good magnetic field proportionality and extremely large product sensitivity
1000V/AT was obtained. Moreover, 5.7V/T
The maximum magnetic flux density sensitivity of (7.5 mA) is a value that cannot be obtained with conventional magnetic sensors.

Figure 6 shows the performance of the heterojunction magnetic sensor (2DEG) of the present invention and the currently used magnetic sensors in terms of product sensitivity K _H , carrier mobility μ _H , and sensitivity figure of merit (K _H μ _H ) ^1/2 , the comparison was made using the relationship of characteristic impedance ρ/t. According to this example, the conditions for high performance that could not be achieved with conventional semiconductor materials are satisfied, and the prototype results as expected are obtained.

As a result of investigating the noise characteristics and temperature characteristics, the noise is approximately
The thermal noise level is reached at 1kHz, and the temperature characteristics are also quite good. In addition, in the AlGaAs/GaAs system, it is necessary to fabricate one with a small Al composition ratio or use super doping.
It is expected to have a small temperature dependence comparable to that of GaAs.

Table 1 summarizes the characteristics of typical prototype Hall elements.

■■■ Turtle Shell [0013] ■■■ [Effects of the Invention] As described above, according to the present invention, a two-dimensional electron gas layer with high mobility is formed in an extremely thin region, and input and output electrodes are connected to this two-dimensional Since it is formed to have ohmic contact with the electronic gas layer at multiple locations, an extremely sensitive and thin magnetic sensor can be obtained, which can greatly contribute to high accuracy and speeding up measurement and control. This excellent effect can be obtained.

[Brief explanation of drawings]

The following drawings all show embodiments of the invention, and the first
The figure is a schematic diagram of the structure of a heterojunction Hall element, Figures 2 and 3 are schematic cross-sectional views and energy band diagrams of the heterojunction Hall element, respectively, and Figures 4 and 5 are the magnetic flux density of the heterojunction Hall element. The Hall voltage characteristic diagram, the input current-Hall voltage characteristic diagram, and FIG. 6 are characteristic diagrams showing the carrier mobility-product sensitivity performance of the heterojunction Hall element of the present invention compared to the conventional element. FIG. 3 is a perspective view when the Hall element shown in FIG. 3 is applied to a magnetic sensor, and FIG. 8 is a partial sectional view of FIG. 7. 2a, 2b... Current terminal, 3a, 3b... Hall terminal, 4... Non-doped GaAs, 5a... Non-doped AlGaAs, 5b... Si-doped AlGaAs, 5
c...Si-doped GaAs, 6...Two-dimensional electron gas layer, 200...Au-Ge ohmic electrode, 201...
...Mesa-shaped hole.

Claims (1)

[Scope of Claims] 1. A heterojunction magnetic sensor including a heterojunction structure in which a two-dimensional electron gas layer with high mobility is formed at the junction of dissimilar semiconductors with different band gaps. A heterojunction magnetic sensor characterized in that input/output electrodes are formed in ohmic contact with a two-dimensional electron gas layer at multiple locations. 2 The heterojunction structure does not contain impurities
A GaAs layer is bonded to an impurity-free AlGaAs layer,
And this AlGaAs layer contains n-type impurities.
A heterojunction magnetic sensor according to claim 1, characterized in that it is configured to join layers.