CN104064243A - Sandwiched parallel connection type PIN type alpha irradiation battery and preparation method thereof - Google Patents

Abstract

The invention discloses a sandwiched parallel connection type PIN type alpha irradiation battery and a preparation method thereof. At present, a nuclear battery has problems of low energy transformation ratio and low output power, and the invention is mainly used to solve the problems. The sandwiched parallel connection type PIN type alpha irradiation battery of the invention comprises an upper PIN junction and a lower PIN junction which are connected in parallel and an alpha radiation source layer. The lower PIN junction comprises an N-type ohmic contact electrode, an N-type highly-doped 4H-SiC substrate, an N-type lightly-doped epitaxial layer, a P-type highly-doped epitaxial layer and a P-type ohmic contact electrode from down to up successively. The structure distribution of the upper PIN junction from top to bottom is the same as the structure distribution of the lower PIN junction from down to up. The alpha radiation source layer is sandwiched between the P-type ohmic contact electrodes of the upper PIN junction and the lower PIN junction so as to realize the full utilization of high-energy alpha particles. According to the invention, advantages of large radiation source and semiconductor contact area, high nuclear raw material utilization rate and energy collection rate and large battery output voltage can be realized, and the battery can be used to supply power to a small circuit in a lasting manner or supply power in unattended occasions which need to be powered for a long time, such as polar regions, desert, etc.

Description

Sandwich parallel PIN type α irradiation battery and preparation method thereof

technical field

The invention belongs to the field of microelectronics, and relates to a structure and a preparation method of a semiconductor device, in particular to a silicon carbide-based sandwich parallel PIN type α irradiation battery and a preparation method thereof, which can be used in micro-circuits such as micro-nano electromechanical systems and aviation Aerospace, deep sea, polar regions and other occasions that require long-term power supply and are unattended.

technical background

With people's demand for low power consumption, long life, high reliability and small size power supply equipment, as well as concerns about nuclear waste disposal, micronuclear batteries have become more and more popular. Due to its outstanding characteristics, micronuclear batteries can be used to solve the long-term power supply problems of micropipe robots, implanted microsystems, wireless sensor node networks, artificial cardiac pacemakers, and portable mobile electronics. And it is expected to replace solar cells and thermoelectric radioisotope batteries, and solve the long-term power supply problems of micro/nano satellites, deep space unmanned probes and ion thrusters in the field of aerospace and aviation.

In 1953, it was discovered by Rappaport that the use of beta (β-Particle) rays produced by isotope decay can generate electron-hole pairs in semiconductors, and this phenomenon is called β-VoltaicEffect. In 1957, Elgin-Kidde first used β-VoltaicEffect in power supply and successfully manufactured the first isotope micro-battery β-VoltaicBattery. Since 2006, with the advancement of wide bandgap semiconductor material SiC preparation and process technology, there have been reports on SiC-based isotope micro-batteries.

Chinese patent CN101325093A discloses a SiC-based Schottky junction nuclear battery proposed by Zhang Lin, Guo Hui and others. Since the Schottky contact layer in the Schottky nodule cell covers the entire battery area, after the incident particles reach the surface of the device, they will be blocked by the Schottky contact layer, and only part of the particles can enter the device, while the particles entering the depletion region It will contribute to the output power of the battery. Therefore, the energy loss of the incident particles in the nuclear battery with this structure is large, and the energy conversion efficiency is low.

The document "Demonstrationofa4HSiCbetavoltaiccell" introduces the silicon carbide PN junction nuclear battery proposed by C.I.Tomas, M.V.S.Chandrashekhar, HuiLi, etc. of Cornell University in New York, USA. The substrate used in this structure is a P-type highly doped substrate, and the existing process of growing an epitaxial layer on the substrate is immature. Therefore, surface defects are easily introduced, the leakage current of the device is large, and the energy conversion rate is low.

The document "Demonstrationofatadiationresistant, highefficiencySiCbetavoltaic" introduced that C.J.Eiting, V.Krishnamoorthy and S.Rodgers, T.George of Qynergy Corporation in New Mexico, USA jointly proposed a silicon carbide p-i-n junction nuclear battery, as shown in Figure 1. From top to bottom, the PIN nuclear battery is as follows: radioactive source 7, P-type ohmic contact electrode 6, P-type highly doped SiC layer 4, P-type SiC layer 3, intrinsic i layer 2, n-type highly doped SiC lining Bottom 1 and N-type ohmic contact electrode 5. In this structure, only the radiation-generated carriers within a minority carrier diffusion length in the depletion layer and its vicinity can be collected. Moreover, in order to prevent the ohmic contact electrode from blocking the incident ions, the P-type ohmic electrode is made at a corner of the device, so that the irradiated carriers far away from the P-type ohmic electrode are recombined during the transport process, which reduces the energy conversion. rate, reducing the output current of the battery.

Contents of the invention

The purpose of the present invention is to address the above-mentioned deficiencies in the prior art, to propose a sandwich parallel PIN type α irradiation battery and its preparation method, to improve the utilization rate of α radiation source, thereby increasing the output current and output voltage of the battery.

Technical scheme of the present invention is realized like this:

One. The sandwich parallel PIN type α radiation battery of the present invention comprises: PIN unit and α radiation source layer, it is characterized in that:

The PIN unit is composed of two upper and lower PIN junctions connected in parallel; the lower PIN junction is in order from bottom to top, N-type ohmic contact electrode 5, N-type highly doped 4H-SiC substrate 1, N-type low-doped epitaxy Layer 2, P-type highly doped epitaxial layer 3 and P-type ohmic contact electrode 4; the upper PIN junction is in order from bottom to top, P-type ohmic contact electrode 4, P-type highly doped epitaxial layer 3, N-type low-doped Epitaxial layer 2, N-type highly doped 4H-SiC substrate 1 and N-type ohmic contact electrode 5;

The α radiation source layer 6 is sandwiched between the P-type ohmic contact electrodes 4 of the upper and lower PIN junctions, so as to fully utilize high-energy α particles.

Preferably, the α-radiation source layer 6 adopts americium element with an atomic mass of 241, namely Am ²⁴¹ .

Preferably, the α radiation source layer 6 is made of plutonium element with an atomic mass of 238, namely Pu ²³⁸ .

As preferably, the thickness h of the alpha radiation source layer 6 satisfies h≤m, wherein m is the average incident depth of the high-energy alpha particles released by the alpha radiation source in the alpha radiation source material, and is Am ²⁴¹ for the alpha radiation source , its value is: m=7.5 μm, and for the alpha radiation source is Pu ²³⁸ , its value is: m=10 μm.

Preferably, the thickness L of the N-type low-doped epitaxial layer 2 satisfies L≥g, wherein g is the average incident depth of the high-energy alpha particles released by the alpha radiation source in 4H-SiC, and for the alpha radiation source is For Am ²⁴¹ , the value is: i=10 μm, for the α radiation source is Pu ²³⁸ , the value is: i=18.2 μm.

Preferably, the substrate 1 is N-type 4H-SiC with a doping concentration of 1×10 ¹⁸ cm ⁻³ , the P-type highly doped epitaxial layer 3 and the N-type low-doped epitaxial layer 2 are both 4H-SiC epitaxial, Wherein the doping concentration of the P-type highly doped epitaxial layer 3 is 1x10 ¹⁹ ~ 5x10 ¹⁹ cm ^-3 , and the thickness is 0.1 ~ 0.2 μm, and the doping concentration of the N-type low doping epitaxial layer 2 is 1x10 ¹⁵ ~ 2x10 ¹⁵ cm ^{-3 3} .

Two. preparation method of the present invention comprises the following steps:

(1) Make the lower PIN knot:

1.1) Cleaning: cleaning the SiC sample to remove surface pollutants;

1.2) Growth of N-type low-doped epitaxial layer: use the chemical vapor deposition CVD method to epitaxially grow a layer of N-type with a doping concentration of 1x10 ¹⁵ ~ 2x10 ¹⁵ cm ^-3 and a thickness of 15 ~ 30 μm on the surface of the cleaned SiC sample. Low-doped epitaxial layer;

1.3) Growth of P-type highly doped epitaxial layer: use chemical vapor deposition CVD method to epitaxially grow a layer of doping concentration on the surface of N-type low-doped epitaxial layer with a doping concentration of 1x10 ¹⁹ ~ 5x10 ¹⁹ cm ^-3 and a thickness of 0.1 ~ 0.2 μm P-type highly doped epitaxial layer;

1.4) Deposit metal ohmic contact electrodes: use electron beam evaporation to deposit a Ni metal layer with a thickness of 300nm on the surface of the P-type highly doped epitaxial layer and the non-epitaxy back of the SiC substrate, as the P-type ohmic contact electrodes and N Type ohmic contact electrode; rapid annealing in nitrogen atmosphere at 1100°C for 3 minutes. .

(2) Repeat step 1.1) to step 1.4) to make the upper PIN junction.

(3) Molecular plating is used to plate an alpha radiation source with a thickness of 3-6 μm on the P-type ohmic contact electrode of the lower PIN junction or the P-type ohmic contact electrode of the upper PIN junction.

(4) The side of the P-type ohmic contact electrode of the upper PIN junction and the side of the P-type ohmic contact electrode of the lower PIN junction are pressed together by bonding to complete the fabrication of the sandwich parallel PIN type α-irradiated battery.

Compared with the prior art, the present invention has the following advantages:

1. Because the bandgap 4H-SiC of the substrate material used in the present invention is larger than that of traditional Si, it has better anti-radiation properties, can reduce the damage of high-energy alpha particles to devices, and improve the working voltage of the battery. At the same time prolong the service life of the battery;

2. In the present invention, since the thickness of the epitaxial N-type low-doped epitaxial layer is not less than the average incident depth of the high-energy alpha particles released by the alpha radiation source in 4H-SiC, the high-energy alpha particles in the N-type low-doped epitaxial layer can be reduced The attenuation of the high-energy alpha particles concentrates in the space charge region near the interface of the P-type highly doped epitaxial layer and the N-type low-doped epitaxial layer, improving the energy conversion rate;

3. In the present invention, since the thickness of the P-type highly doped epitaxial layer is 0.1-0.2 μm, the thickness of the α-radiation source layer is not greater than twice the average incident depth of the high-energy α particles released by the α-radiation source in the α-radiation source material , can reduce the attenuation of high-energy α particles in the P-type highly doped epitaxial layer and α-radiation source layer, and improve the energy collection rate;

4. Since the present invention sandwiches the α radiation source layer between the P-type ohmic contact electrodes of the upper and lower PIN junctions, compared with the prior art where the radiation source layer is placed on the upper surface of the battery, the α radiation source material is saved. Improve the utilization rate of alpha radiation source, thereby improving the energy utilization rate of the battery;

5. The present invention improves the output voltage of the battery due to the parallel placement of two PIN junctions.

Description of drawings

Fig. 1 is the cross-sectional schematic view of existing PIN nuclear battery;

Fig. 2 is a schematic cross-sectional view of a sandwich parallel PIN type α irradiation battery of the present invention;

Fig. 3 is a schematic flow chart of manufacturing a sandwich parallel PIN type α-irradiated battery according to the present invention.

Detailed ways

Referring to Fig. 2, the irradiation battery of the present invention includes: a PIN unit and an alpha radiation source layer, the PIN unit is composed of upper and lower two PIN junctions connected in parallel; the lower PIN junction is sequentially from bottom to top, N-type ohmic contact electrode 5 , N-type highly doped 4H-SiC substrate 1, N-type low-doped epitaxial layer 2, P-type highly doped epitaxial layer 3, and P-type ohmic contact electrode 4; the upper PIN junction is in order from bottom to top, P-type Ohmic contact electrode 4, P-type highly doped epitaxial layer 3, N-type low-doped epitaxial layer 2, N-type highly doped 4H-SiC substrate 1 and N-type ohmic contact electrode 5; α radiation source layer 6 is sandwiched between the upper and lower Between the P-type ohmic contact electrodes 4 of the two PIN junctions, the thickness h satisfies h≤m, where m is the average incident depth of the high-energy alpha particles released by the alpha radiation source in the alpha radiation source material, and for the alpha radiation source is For Am ²⁴¹ , the value is: m=7.5 μm, for the α radiation source is Pu ²³⁸ , the value is: m=10 μm.

When the battery is in working condition, the high-energy alpha particles emitted from the alpha radiation source layer 6 pass through the P-type ohmic contact electrode 4 of the upper and lower PIN junctions and inject into the P-type highly doped epitaxial layer 3 and the N-type low-doped epitaxial layer 3. The space charge region near the layer 2 interface excites the carriers and forms the output current.

Referring to Fig. 3, the method for making a sandwich parallel PIN type α-irradiated battery according to the present invention provides the following three embodiments:

Example 1, preparing a sandwich parallel PIN type α radiation battery with Am ²⁴¹ as the α radiation source and 6 μm thickness of the radiation source layer.

Step 1: Make the lower PIN knot.

(1.1) Clean the 4H-SiC sample to remove surface pollutants, as shown in Figure 3(a).

(1.1.1) Soak a highly doped n-type 4H-SiC substrate sample with a doping concentration of lx10 ¹⁸ cm ^-3 in NH ₄ OH + H ₂ O ₂ reagent for 10 minutes, take it out and dry it to remove the sample surface organic residues;

(1.1.2) Soak the 4H-SiC sample after removing the surface organic residues with HCl+H ₂ O ₂ reagent for 10 minutes, take it out and dry it to remove ionic pollutants.

(1.2) Epitaxial growth of an N-type low-doped epitaxial layer, as shown in FIG. 3( b ).

A nitrogen-doped N-type doped epitaxial layer is epitaxially grown on the cleaned SiC sample by chemical vapor deposition CVD. The process conditions are: the epitaxy temperature is 1570°C, the pressure is 100mbar, the reaction gas is silane and propane, the carrier gas is pure hydrogen, the magazine source is liquid nitrogen, and the nitrogen doping concentration is 1x10 ¹⁵ cm ^-3 , and the thickness is 15μm. N-type low-doped epitaxial layer.

(1.3) Epitaxial growth of a P-type highly doped epitaxial layer, as shown in FIG. 3(c).

On the grown N-type low-doped epitaxial layer, the aluminum-doped P-type highly-doped epitaxial layer is epitaxially grown by chemical vapor deposition CVD. The process conditions are: the epitaxy temperature is 1570°C, the pressure is 100mbar, and the reaction gas Silane and propane, the carrier gas is pure hydrogen, and the impurity source is trimethylaluminum to obtain a P-type highly doped epitaxial layer with an aluminum doping concentration of 1×10 ¹⁹ cm ^-3 and a thickness of 0.1 μm.

(1.4) Deposit ohmic contact electrodes, as shown in Figure 3(d).

(1.4.1) Perform RCA standard cleaning on the SiC sample after the growth of the P-type highly doped epitaxial layer;

(1.4.2) Put the cleaned sample on the glass slide in the electron beam evaporation coating machine, adjust the distance from the glass slide to the target to 50cm, and pump the pressure of the reaction chamber to 5×10 ^-4 Pa, adjust The beam current is 40mA, and a Ni metal layer with a thickness of 300nm is deposited on the surface of the P-type highly doped epitaxial layer of the SiC sample as a P-type ohmic contact electrode;

(1.4.3) Deposit a Ni metal layer with a thickness of 300nm on the non-epitaxy backside of the SiC substrate by electron beam evaporation as an N-type ohmic contact electrode.

(1.4.4) Rapid annealing in nitrogen atmosphere for 3 minutes at 1100°C.

Step 2: Make the upper PIN knot.

Repeat step (1.1) to step (1.4) to get the upper PIN junction.

Step 3: Use molecular plating to plate a layer of α radiation source with a thickness of 6 μm on the P-type ohmic contact electrode of the lower PIN junction, as shown in FIG. 3( e ).

Step 4: Using the bonding method, press together the α-radiation source layer on the P-type ohmic contact electrode of the upper PIN junction and the P-type ohmic contact electrode of the lower PIN junction to obtain a sandwich parallel PIN-type α-irradiated battery, as shown in Figure 3(f) shows.

Example 2, preparing a sandwich parallel PIN type α radiation battery with Am ²⁴¹ as the α radiation source and 5 μm thickness of the radiation source layer.

Step 1: Make the lower PIN knot.

1a) Clean the 4H-SiC sample to remove surface pollutants, as shown in Figure 3(a).

This step is the same as step (1.1) of Example 1.

1b) Epitaxial growth of an N-type low-doped epitaxial layer, as shown in Figure 3(b).

A nitrogen-doped N-type doped epitaxial layer is epitaxially grown on the cleaned SiC sample by chemical vapor deposition CVD. The process conditions are: the epitaxy temperature is 1570°C, the pressure is 100mbar, the reaction gas is silane and propane, the carrier gas is pure hydrogen, the magazine source is liquid nitrogen, the complete nitrogen doping concentration is 1.5x10 ¹⁵ cm ^-3 , and the thickness is 25μm Growth of N-type low-doped epitaxial layer.

1c) Epitaxial growth of a P-type highly doped epitaxial layer, as shown in Figure 3(c).

On the grown N-type low-doped epitaxial layer, a P-type highly-doped epitaxial layer doped with aluminum ions was epitaxially grown by chemical vapor deposition CVD. It is silane and propane, the carrier gas is pure hydrogen, and the impurity source is trimethylaluminum, and the growth of a P-type highly doped epitaxial layer with an aluminum doping concentration of 3x10 ¹⁹ cm ^-3 and a thickness of 0.15 μm is completed.

1d) Deposit metal contact electrodes, as shown in Figure 3(d).

This step is the same as step (1.4) of Embodiment 1.

Step 2: Make the upper PIN knot.

Repeat steps 1a) to 1d) to obtain the upper PIN junction.

Step 3: use molecular plating to plate a layer of α radiation source with a thickness of 5 μm on the P-type ohmic contact electrode of the upper PIN junction, as shown in FIG. 3( e ).

Step 4: Using the bonding method, the α radiation source layer on the P-type ohmic contact electrode of the upper PIN junction is pressed together with the P-type ohmic contact electrode of the lower PIN junction to obtain a sandwich parallel PIN-type α-irradiated battery, such as Figure 3(f) shows.

Example 3, preparing a sandwich parallel-connected PIN type α-irradiated battery whose α-radiation source layer is Pu ²³⁸ , and the thickness of the α-radiation source layer is 3 μm.

Step A: Make the upper PIN knot.

(A1) Clean the 4H-SiC sample to remove surface contamination, as shown in Figure 3(a).

This step is the same as step (1.1) of Example 1.

(A2) Epitaxially grow a nitrogen-doped N-type low-doped epitaxial layer on the cleaned SiC sample by chemical vapor deposition CVD. The process conditions are as follows: the epitaxy temperature is 1570°C, the pressure is 100mbar, the reaction gas is silane and propane, the carrier gas is pure hydrogen, and the magazine source is liquid nitrogen. An N-type low-doped epitaxial layer with a nitrogen doping concentration of 2x10 ¹⁵ cm ^-3 and a thickness of 30 μm is obtained as shown in Figure 3(b).

(A3) A P-type highly doped epitaxial layer doped with aluminum ions is epitaxially grown on the grown N-type low-doped epitaxial layer by chemical vapor deposition CVD method, and the process conditions are: the epitaxy temperature is 1570°C, and the pressure is 100mbar , the reaction gas is silane and propane, the carrier gas is pure hydrogen, and the impurity source is trimethylaluminum, the P-type highly doped epitaxial layer with an aluminum doping concentration of 5x10 ¹⁹ cm ^-3 and a thickness of 0.2 μm is obtained as shown in Figure 3 ( c).

(A4) Deposit metal contact electrodes, as shown in Figure 3(d).

This step is the same as step (1.4) of Embodiment 1.

Step B: Make the upper PIN knot.

Repeat step (A1) to step (A4) to obtain the upper PIN junction.

Step C: use molecular plating to plate a layer of α-radiation source with a thickness of 3 μm on the P-type ohmic contact electrode of the upper PIN junction and the P-type ohmic contact electrode of the lower PIN junction, as shown in Figure 3(e).

Step D: Laminate the α-radiation source layer on the P-type ohmic contact electrode of the upper PIN junction with the α-radiation source layer on the P-type ohmic contact electrode of the lower PIN junction to obtain a sandwich parallel PIN-type α-irradiated battery , as shown in Figure 3(f).

Claims (7)

1. a sandwich parallel PIN type alpha irradiation battery, comprising: PIN unit and αsource layer, is characterized in that:

Described PIN unit, adopts by the parallel connection of upper and lower two PIN knot and forms; Lower PIN knot is followed successively by from bottom to top, N-type Ohm contact electrode (5), the highly doped 4H-SiC substrate of N-type (1), the low-doped epitaxial loayer of N-type (2), the highly doped epitaxial loayer of P type (3) and P type Ohm contact electrode (4); Upper PIN knot is followed successively by from bottom to top, P type Ohm contact electrode (4), the highly doped epitaxial loayer of P type (3), the low-doped epitaxial loayer of N-type (2), the highly doped 4H-SiC substrate of N-type (1) and N-type Ohm contact electrode (5);

Described αsource layer (6), is clipped between the P type Ohm contact electrode (4) of upper and lower two PIN knot, to realize making full use of high-energyα-particle.

2. battery according to claim 1, is characterized in that αsource layer (6) adopts the americium element that atomic mass is 241, i.e. Am ²⁴¹.

3. battery according to claim 1, is characterized in that αsource layer (6) adopts the plutonium element that atomic mass is 238, i.e. Pu ²³⁸.

4. according to the battery described in claim 1 or 2 or 3, the thickness h that it is characterized in that αsource layer (6) meets h≤m, the average incident degree of depth of the high-energyα-particle that wherein m discharges for αsource in αsource material is Am for αsource ²⁴¹, its value is: m=7.5 μ m is Pu for αsource ²³⁸, its value is: m=10 μ m.

5. according to the battery described in claim 1 or 2 or 3, the thickness L that it is characterized in that the low-doped epitaxial loayer of N-type (2) meets L>=g, wherein, the average incident degree of depth of the high-energyα-particle that g discharges for αsource in 4H-SiC, is Am for αsource ²⁴¹, its value is: i=10 μ m is Pu for αsource ²³⁸, its value is: i=18.2 μ m.

6. battery according to claim 1, is characterized in that it is l x10 that substrate (1) adopts doping content ¹⁸cm ^-3n-type 4H-SiC, the highly doped epitaxial loayer of P type (3) and the low-doped epitaxial loayer of N-type (2) are 4H-SiC extension, wherein the doping content of the highly doped epitaxial loayer of P type (3) is 1x10 ¹⁹～5x10 ¹⁹cm ^-3, thickness is 0.1～0.2 μ m, the doping content of the low-doped epitaxial loayer of N-type (2) is 1x10 ¹⁵～2x10 ¹⁵cm ^-3.

7. a preparation method for sandwich parallel PIN type alpha irradiation battery, comprises the following steps:

(1) make lower PIN knot:

1.1) clean: SiC print is cleaned, to remove surface contaminant;

1.2) the low-doped epitaxial loayer of growth N-type: utilizing the SiC print surface epitaxial growth one deck doping content of chemical vapor deposition CVD method after cleaning is 1x10 ¹⁵～2x10 ¹⁵cm ^-3, thickness is the low-doped epitaxial loayer of the N-type of 15～30 μ m;

1.3) the highly doped epitaxial loayer of growing P-type: utilizing chemical vapor deposition CVD method is 1x10 in the low-doped epi-layer surface epitaxial growth of N-type one deck doping content ¹⁹～5x10 ¹⁹cm ^-3, thickness is the highly doped epitaxial loayer of P type of 0.1～0.2 μ m;

1.4) deposit Ohm contact electrode: utilize electron-beam vapor deposition method at the highly doped epi-layer surface of P type and the SiC substrate Ni metal level that back side deposition thickness of extension is not 300nm, respectively as P type Ohm contact electrode and N-type Ohm contact electrode; Short annealing 3 minutes in nitrogen atmosphere at 1100 DEG C.

(2) repeating step 1.1) to step 1.4) PIN ties in makings.

(3) utilize molecular plating the P type Ohm contact electrode of lower PIN knot or on plate the αsource that a layer thickness is 3～6 μ m on the P type Ohm contact electrode of PIN knot.

(4) utilize bonding method that the P type Ohm contact electrode one side of upper PIN knot and the P type Ohm contact electrode one side of lower PIN knot are pressed together, complete the making of sandwich parallel PIN type alpha irradiation battery.