SOI Bipolar Transistors With Isolation Trenches for ESD Protection
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Solution Overview
Problem
In FDSOI technology, it is challenging to produce transistors with distinct threshold voltages due to minimal channel doping, making it difficult to differentiate threshold voltages and requiring costly and complex methods, and there is a need for effective protection against electrostatic discharges without compromising the compactness of integrated circuits.
Innovation Solution
The use of isolating trenches of varying depths and dimensions in integrated circuits of SOI type to create bipolar transistors, along with a biased ground plane, allows for the modulation of threshold voltages and enhanced protection against electrostatic discharges by controlling the doping of the ground planes and their bias.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If different gate materials are used to produce transistors with distinct threshold voltages in FDSOI technology, then threshold voltage differentiation is achieved, but manufacturing complexity and cost increase significantly
Solution Approach 1:
The patent applies local quality by creating isolating trenches with different depths (first trenches extending to the buried oxide layer, second trenches extending only to the thin oxide layer) in different regions of the semiconductor substrate. This localized structural differentiation enables threshold voltage modulation without changing gate materials, resolving the contradiction between achieving distinct threshold voltages and maintaining manufacturing simplicity.
Solution Approach 2:
The patent changes physical parameters by varying the depth and dimensions of isolating trenches rather than changing material composition. By adjusting trench depth, width, and spacing, the patent achieves different threshold voltages for transistors in different regions, avoiding the need for different gate materials and thus reducing manufacturing complexity while maintaining threshold voltage differentiation capability.
2Reliability
If isolating trenches are used to electrically isolate transistors, then electrical isolation is achieved, but integration density is reduced
Solution Approach 1:
The patent segments the isolating trench structure into two distinct types with different depths: first trenches that extend through the thin oxide layer to the buried oxide layer for complete electrical isolation, and second trenches that extend only to the thin oxide layer for partial isolation. This segmentation allows optimized isolation where needed while minimizing isolation overhead in other regions, thus improving integration density while maintaining necessary electrical isolation.
Solution Approach 2:
The patent introduces depth as an additional dimension for controlling isolation characteristics. By varying trench depth along the vertical dimension rather than only using planar separation, the patent achieves effective electrical isolation with reduced lateral footprint, thereby improving integration density while maintaining reliability.
3Reliability
If the depth of isolating trenches is increased to improve electrostatic discharge protection, then protection effectiveness is enhanced, but manufacturing precision requirements increase
Solution Approach 1:
The patent segments the trench depth requirements into two levels: deep first trenches for transistors requiring maximum electrostatic discharge protection (extending to the buried oxide layer), and shallower second trenches for transistors where complete isolation is less critical. This segmentation allows differentiated protection levels without uniformly increasing manufacturing precision requirements across the entire substrate.
Solution Approach 2:
The patent applies local quality by providing enhanced electrostatic discharge protection (deeper trenches) only in specific regions where transistors are most vulnerable, rather than uniformly deep trenches across the entire chip. This localized approach improves protection effectiveness where needed while maintaining reasonable manufacturing precision requirements overall.
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 enables the production of transistors with distinct threshold voltages while providing effective protection against electrostatic discharges, reducing overcurrent and improving integration density, thus addressing the limitations of existing technologies in FDSOI technology.
Implementation Method 1
By acting on the doping of the ground planes and on their bias, a range of threshold voltages can be defined for the different transistors
Implementation Method 2
the transistors are generally surrounded by the isolating trenches (referred to by the acronym STI, for 'Shallow Trench Isolation') which extend to the wells
Implementation Method 3
such integrated circuits also include devices protecting against accidental electrostatic discharges (ESD) that can damage these transistors
Data Source
AI summary
An integrated circuit includes a semiconductor substrate, a silicon layer, a buried isolating layer arranged between the substrate and the layer, a bipolar transistor comprising a collector and emitter having a first doping, and a base and a base contact having a second doping, the base forming a junction with the collector and emitter, the collector, emitter, base contact, and the base being coplanar, a well having the second doping and plumb with the collector, emitter, base contact and base, the well separating the collector, emitter and base contact from the substrate, having the second doping and extending between the base contact and base, a isolating trench plumb with the base and extending beyond the layer but without reaching a bottom of the emitter and collector, and another isolating trench arranged between the base contact, collector, and emitter, the trench extending beyond the buried layer into the well.