Radiation Hardened Bipolar Junction Transistor Insulator
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Bipolar junction transistors are sensitive to mobile charges in insulating layers, particularly due to ionizing radiation, which causes uncontrolled variations in electrical parameters like DC forward current gain, especially in applications exposed to cosmic radiation and solar winds, and existing radiation hardening techniques are not completely satisfactory.
Innovation Solution
A method for integrating bipolar junction transistors with a planar thin insulating layer, where a sacrificial insulating layer is removed and replaced with a thinner radiation-hardened intermediate layer, and an extrinsic base region with higher impurity concentration is formed, along with a field plate to control the electric field and hole accumulation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a thick insulating layer is used to cover the front surface of the die, then the transistor structure is well protected and manufactured, but mobile charges accumulate in the layer causing uncontrolled variations in electrical parameters like DC forward current gain
Solution Approach 1:
The patent changes the thickness parameter of the insulating layer from conventional thick to ultrathin (few nanometers), fundamentally altering the charge accumulation behavior. This parameter change transforms the insulating layer from a charge-trapping volume to a charge-repelling barrier, eliminating mobile charge accumulation while maintaining electrical isolation functionality.
Solution Approach 2:
The patent employs composite material structure with the ultrathin insulating layer positioned between the base region and the metal contact. This composite approach combines the electrical isolation properties of the insulator with the conductivity of adjacent doped regions, creating a functional assembly that prevents charge accumulation while maintaining proper transistor operation.
2Reliability
If radiation hardening techniques are applied to make bipolar transistors resistant to ionizing radiations, then reliability in radiation environments improves, but device complexity and manufacturing difficulty increase
Solution Approach 1:
The patent extracts and eliminates the problematic thick insulating layer that causes charge accumulation, replacing it with an ultrathin version. This extraction of the harmful element (thick insulator) while retaining the essential function (electrical isolation) simplifies the device structure and reduces manufacturing complexity compared to conventional radiation hardening techniques that add complex protective structures.
Solution Approach 2:
The patent applies local quality enhancement by creating highly doped regions (n+ and p+) at specific locations - the emitter contact region and the base contact region. These localized high-doping areas provide radiation hardness precisely where needed, rather than requiring complex global structural modifications throughout the entire transistor.
3Reliability
If the insulating layer thickness is reduced to minimize hole trapping, then radiation hardness improves, but manufacturing precision requirements increase
Solution Approach 1:
The patent applies preliminary action by forming highly doped regions (n+ emitter contact and p+ base contact) adjacent to the ultrathin insulating layer before final assembly. These pre-formed doped regions create strong electric fields that actively repel mobile charges from the insulating layer, providing a proactive mechanism that compensates for any variations in insulator thickness and ensures consistent radiation hardness across manufacturing batches.
Solution Approach 2:
The patent utilizes parameter changes in the doping concentration (creating n+ and p+ high-doping regions) to enhance the electric field strength at the insulator interfaces. This parameter modification in the adjacent regions provides a buffer that maintains device performance even when insulating layer thickness varies within manufacturing tolerances, reducing the stringency of thickness control requirements.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach minimizes hole trapping, reduces base-to-emitter leakage current, and maintains base-emitter breakdown voltage, resulting in a radiation-hardened transistor with stable electrical characteristics and high insensitivity to ionizing radiation, suitable for applications with strict radiation hardening requirements.
Implementation Method 1
The corresponding positive charge in the insulating layer creates an inverting layer (with a negative charge) in P-type regions at the front surface of the die
Implementation Method 2
when particles or electromagnetic waves with sufficiently high energy (such as γ-rays) strike the die, they cause the detachment of electrons from their atoms in the insulating layer, so as to create corresponding free electron-hole pairs
Implementation Method 3
Due to the high mobility of the free electrons in the insulating layer, they drift very fast and recombine at the terminals of the bipolar transistors
Data Source
Figure 1A~1C
Figure 1D~1F
Figure 1G~1I
AI summary
A method is proposed for integrating a bipolar injunction transistor (100) in a die of semiconductor material having a main surface (105) covered by a sacrificial insulating layer (110), the die including a collector region (Rc) of a first type of conductivity extending from the main surface. The method includes the steps of forming an intrinsic base region (Rbi) of a second type of conductivity extending in the collector region from the main surface through an intrinsic base window (Wbi) of the sacrificial insulating layer, and forming an emitter region (Re) of the first type of conductivity extending in the intrinsic base region from the main surface through an emitter window (We) of the sacrificial insulating layer; in the solution according to an embodiment of the invention, the method further includes the steps of removing the sacrificial insulating layer, forming an intermediate insulating layer (115) on the main surface, the intermediate insulating layer having a thickness lower than a thickness of the sacrificial layer, and forming an extrinsic base region (Rbe) of the second type of conductivity extending in the intrinsic base region from the main surface through an extrinsic base window (Wbe) of the intermediate insulating layer, the extrinsic base region having a concentration of impurities higher than a concentration of impurities of the intrinsic base region and being separated from the emitter region by a portion of the intrinsic base region.