JPS6354785A - Hetero-junction magnetic sensor - Google Patents

Abstract

PURPOSE:To obtain a magnetic sensor which has high mobility and an extremely thin film by forming a secondary electron gas layer and input/output electrodes having a plurality of ohmic contacts. CONSTITUTION:A secondary electron gas layer 6 and input/output electrodes 200 having ohmic contacts at a plurality of positions are formed in a hetero junction magnetic sensor having a hetero junction structure that the layer 6 of high mobility is formed at the junction of different type semiconductors 4, 5 of different band gaps. For example, a non-doped GaAs layer 4, a non-doped AlGaAs layer 5a, an Si-doped AlGaAs layer 5a, an Si-doped GaAs layer 5c are sequentially formed by an MBE on a semi-insulating GaAs substrate 7, and the layer 6 is formed on a boundary of the side of the layer 5 of the layer 4. The electrodes 200 which perform the function of the electrodes of a current terminal and a hole terminal are formed to have ohmic contacts with the layers 4, 5a, 5b, 5c.

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) Conventionally, Si has been used as a semiconductor material for magnetic sensors.

Ge or compound half-doors InSb, InA, s, G
Single crystal thin plates such as aAs, vapor deposited films, epitaxial films,
Ion implanted layers are commonly used.

However, each of the above semiconductor materials had drawbacks.

That is, in order to improve the performance of magnetic sensors, ultra-thin film materials with high mobility are required, but indium antimony (InSb), which provides high mobility, is difficult to make into ultra-thin films, and gallium arsenide (G a Since it is difficult to increase the mobility of ultrathin films with silicon (Si) and silicon (Si), there is a technical limit to achieving high 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.

■□=to, BI ■KH...(1)-(
W/ri)μHBV"μ, ... (2) = <wK
n μ / 7ri l/28 P l/2” (KHμ
) l/2...(3) Here, J, w and t are
The length, width, thickness I, V, and P of the element are the input current, input voltage, and input power.

B is magnetic flux density. K□ is the product sensitivity (=Ro/l=1/n
s e i PH is the Hall coefficient. n is the carrier surface density. e is electron charge), μm is hole mobility.

Since the maximum output is obtained for the maximum input, the sensitivity figure of merit M S F (Magnetic-
fieldSensitive figure of
MSF−(KNμ)
l/2 = +'H(ρ/e)"2 ocμ8 ... (4) Here, ρ-1/ne eμ. Considering the compatibility between the element and the external circuit, the characteristic impedance ρ/l is usually , 10Ω
It is desirable that the resistance is in the range of 10 to 10Ω. In order to increase the sensitivity of the Hall element, it is better to have higher mobility and product sensitivity under these conditions. Since the product sensitivity is proportional to the reciprocal of the carrier areal density (product of carrier density and thickness), 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) be high. Taking Hall output and thermal noise v9, S/
Defining the N ratio, S/N=Vo/VM = (w/j2) ps B (P/4kT)""
xμH...(5) Here, k is Boltzmann's constant. T is the element temperature. In order to increase the S/N, the first thing to do is to have a large μI.
It is a condition.

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 IOKΩ), It has been found that a structure in which high-mobility carriers are confined in an extremely thin active layer is required.

Therefore, in the present invention, by providing a heterojunction structure of two types of semiconductors with different band gaps, for example, AlGaAs and GaAs, a two-dimensional electron gas layer is formed in which electrons are confined in a narrow region of the boundary. In addition to using it as an active layer of a magnetic sensor, 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, a two-dimensional electron gas layer 6 with high mobility is formed at the heterojunction between the two types of semiconductor layers 4 and 5 having different band gaps. In addition,
2a in FIG.

2b is a current terminal for flowing current to the Hall element H, 3a
, 3b are Hall terminals for extracting the Hall electromotive force ■□ generated when a magnetic field of magnetic flux density B is applied to the Hall element H.

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

Figure 2 shows A I G a A s / G a A
s shows the structure of a heterojunction semiconductor, semi-insulating S
, 1. - Non-doped GaAs on the GaAs base plate 7
4. Non-doped AffQaAs5a, Si-doped Al
GaAs 5b and Si-doped GaAs 5c were sequentially formed using molecular beam crystal growth (MBE).

Note that other methods such as organometallic vapor phase epitaxy, liquid phase epitaxy, etc. may also be used.

As can be seen from this figure 2, the two-dimensional electron gas layer 2DE
G6 is non-doped AlG of non-doped GaAs layer 4
It is formed on the boundary surface on the aAs layer 5 side. In addition, non-dope Aj! The reason for providing the GaAs layer 5 is that the Si in the n-type Si-doped AlGaAsSb is
This is to prevent entry into the aAsd.

Further, the Au-Ge ohmic electrodes 200 functioning as electrodes of the current terminals 2a, 2b and the hall terminals 3a, 3b are provided in each layer 4. It is formed to have ohmic contact with 5a, 5b, and 5'c.

For cleaning semi-insulating GaAs substrates for crystal growth, use a mixed solution of concentrated sulfuric acid, hydrogen peroxide, and pure water (with a volume ratio of 4
Etching was carried out for about 1 minute in a liquid temperature of 60 degrees Celsius), and thermal etching was carried out in a vacuum chamber for crystal growth while applying arsenic vapor.

Representative examples of crystal growth conditions are as follows.

1. Ga flux: 6 x 10-' Torr
2, As Franks: 1.2 X 10-' To
rr3, A1 Franks: 1.4 X 10-'
Torr4, crystal growth temperature: 630 degrees Celsius5, crystal growth rate: 1.2 μm/hr (
CaAs) 1.65 μm/hr (A I Ga As ) 6, 1st layer: Non-doped GaAs (500 nm) 2nd layer
Layer: Non-doped AlGaAs (15 nm) 3rd layer; S
i-doped A'ffGaAs (100 nm) 4th layer: S
i-doped GaAs (10 nm) where the St doping concentration is 1 x 10 cm arch.

7. Ohmic electrode is AuGe (7% to 12%)
/ N t / Au due to alloying of the deposited film.

Figure 3 shows the energy band of the prototype heterojunction Hall element. The two-dimensional electron gas layer is made of Si-doped A6
Filled with electrons supplied from GaAs, AffG
If there are too many carriers in the aAs layer, that is, if the amount of impurities is too large or if the AlGaAs layer is too thick,
Current also flows through the AlGaAs layer having surplus carriers with low electron mobility. This reduces the Hall output.

Therefore, it is important to fabricate a heterojunction semiconductor so as to eliminate excess carriers in the AJGaAs layer.

7 and 8 show a specific example in which the Hall element having the above configuration is applied to a specific magnetic sensor. In this example, the A
A large number of mesa-shaped holes 201 are provided in the u-Ge ohmic electrode 2°O, and the metal thin film 200 is brought into direct contact with the two-dimensional electron gas layer 6 to ensure hawk mobility, thereby improving the linearity of the current-voltage characteristics. can be improved. Furthermore, by adopting the above structure, many irregularities are created at the boundary between the ohmic electrode 200 and the semiconductor layers 4 and 5, so the shape effect of the Hall element becomes smaller compared to the conventional uniform electrode structure. Large hall output can be obtained.

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 hemisofavage [R air sensor]. This is GaA
twice that of the epitaxial single crystal of S, and three times that of the same ion-implanted film.
The performance is more than twice that of Si, and about 10 times more excellent than that of Si. In addition, one of the features of the present invention is that the heterojunction hemisphere for magnetic sensors can be used for high-speed transistors (for example, HEM).
T) is similar as a material, and it is possible to integrate a sensor and a signal processing transistor on the same substrate. Due to its low noise level and good temperature characteristics, it is a high-performance magnetic sensor I that cannot be obtained using conventional semiconductor materials.
C is expected to be developed, 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 have a length of 346μm and a width of 200μm.
The electrical characteristics of a cruciform heterojunction Hall element of m are shown. Good magnetic field proportionality, extremely large product sensitivity 1000V/AT
was gotten. Moreover, the maximum magnetic flux density sensitivity of 5.7 V/T (7.5 mA) is a value that cannot be obtained with conventional magnetic sensors.

Figure 6 shows a heterojunction magnetic sensor (2DEG) of the present invention.
(The performance of the n-air sensor is expressed as the product sensitivity KH,
Carrier mobility μm, sensitivity figure of merit (KM μ)
The comparison is made using the relationship of l/2 and characteristic impedance ρ/L. According to this example, the conditions for high performance that could not be achieved with conventional semi-oligolytic materials are satisfied,
The prototype results are as expected.

As a result of examining the noise characteristics and temperature characteristics, the noise reached the thermal noise level at approximately 1 kHz, and the temperature characteristics were also found to be quite good. Also, A/! G a As / G a A
In the s system, a small temperature dependence equivalent to that of GaAs can be expected by manufacturing a material with a small composition ratio of /l or by superdoping.

Table 1 summarizes the characteristics of typical prototype Hall elements.

Table 1 with blank space below [Effects of the Invention] As described above, according to the present invention, a two-dimensional electron gas layer with high mobility is formed in the three pole regions, and a plurality of input/output electrodes are connected to this two-dimensional electron gas layer. Since it is formed to have ohmic contact at certain points, it is possible to obtain an extremely sensitive and thin magnetic sensor, which has the excellent effect of greatly contributing to high accuracy and speeding up of measurement and control. can get.

[Brief explanation of drawings]

The following drawings all show embodiments of the present invention, and FIG. 1 is a schematic configuration diagram of a heterojunction Hall element, and FIGS. 2 and 3 are
4 and 5 are magnetic flux density-Hall voltage characteristic diagrams and input current-Hall voltage characteristic diagrams of the heterojunction Hall element, and FIG. 6 is the conventional one. 7 is a characteristic diagram showing the carrier mobility-product sensitivity performance of the heterojunction Hall element of the present invention with respect to the element, FIG. 7 is a perspective view when the Hall element shown in FIGS. 1 to 3 is applied to a magnetic sensor, and FIG. The figure is a partial sectional view of FIG. 7. 2a, 2b... Current terminal, 3a, 3b... Hall terminal, 4... Non-doped GaAs, 5a... Non-doped AI! 'GaAs, 5b・=St doped Aj2Ga
As. 5C...Si-doped GaAs, 6...Two-dimensional electron gas layer, 200-Au-Ge ohmic electrode, 201...
Mesa-shaped hole. Attorney: Takashi Okabe Figure 1 Figure 2 Figure 3 Carrier frame movement s (m/v, s) Figure 6 Hall voltage v, (v)

Claims (2)

[Claims] (1) At the junction of different types of semiconductors with different band gaps,
In a heterojunction magnetic sensor including a heterojunction structure that forms a two-dimensional electron gas layer with high mobility, this heterojunction magnetic sensor includes input and output electrodes that have ohmic contact with the two-dimensional electron gas layer at multiple locations A heterojunction magnetic sensor characterized in that: (2) The heterojunction structure is made of impurity-free CaA
The heterojunction according to claim 1, characterized in that the s-layer is bonded to an AlGaAs layer containing no impurities, and the AlGaAs layer containing n-type impurities is bonded to this AlGaAs layer. magnetic sensor.